Hello everyone, New DM here, Have only hosted 3... 4 sessions total, and been a player for around 9 sessions.

So, The campaign I'm wanting to run will involve going to a lot of places, to get magical things for the main goal, but I find myself with 3 problems.

1: I'm not sure how many unique places is good, I mean, Having a unique town/hamlet at every stop is great, but I dont want an entire list of things to manage like, "This is town [a] connected to hamlet [b] and town [c], they have a unique history about [yada-yada-yada] and they're well known for [building]" every time the party arrives just to refresh and roleplay.

So what I think I'm asking is, how many lesser stops is good before a unique or important place?

2: What are good ways to keep players engaged with the unique or important places they visit, of course, roping their backstory into it is best or important, but overuse can be proven poorly, so just incase I want to know other methods for players to be engaged with some of the places they visit, anything helps.

Thank you for reading, and hopefully offering support/ideas.

The first advice I’d have to a new player and DM is to run a published campaign first, beginning to end. It can really help you understand these kinds of questions. 

But that wasn’t what you asked, so here goes. Everyone who’s done world building will tell you some of the same things. One is start small. Don’t make the entire world. Make the town the PCs are in, and it’s surrounding environs. Have a vague idea of what else is around, but the further away you go, the less detail to use. Partly, this is because it leaves you wiggle room once they start traveling. You can decide something is a forest right before they get there and run with it if that will make more sense for the story. 
The other reason to keep it vague is part of another thing people will tell you. Players will not interact with or care about 90% of the lore you create. If you find it fun, great, do it for you. Just don’t expect them to care where the stone for the church came from, or that the shopkeepers wife is cheating on him. 

What they will do, every time, is seize on some throwaway description you didn’t mean to be anything, and decide that is absolutely critical. So roll with it when they do. 

I'd like to start this off by saying that most of the advice I will present can be found in many different places across the internet and books, but this podcast by Brennan Lee Mulligan and Matt Mercer creates excellent points. 

To figure out the answer to point 1, you need to first answer point 2 (to some extent). The settlement needs a defining feature that will make sense according to it's location (usually this is the easiest thing to use). For example, a town located in a mountain passage may be a great mining settlement. This is a great basis, as then you can expand on that idea - the mining could probably cause them to mine precious gems as well as metals, meaning the town could be richer than first presumed, as they sell off the materials to a nearby village who can then refine the ores, selling that product off to the major city in the area. This already creates a network that doesn't need to be fully fleshed out, just a brief summary of sorts that keeps settlements connected and gives them a purpose. 

In terms of the 'this settlement is known for ....' repetition, you don't actually have to say it. Let the overwhelming sound of clanging and thumping tell the players that this is a mining town, or maybe it's the pile of rocks and ores on carts ready to leave in the direction of the village that refines them. It goes back to the age-old literary advice: show, don't tell. 

For point 2, that comes into the first point I made: the reason for the settlement is the thing that should draw them in. Perhaps the party has been tasked with obtaining a rare gemstone from the mountains in order for a ceremony to be carried out. They would then travel to our mountain pass settlement, and try to mine or buy this gem. This could come with learning who people are in the town, where the best places to mine are, who in the village can be paid off to do it for them etc. If the gem needs refining, then they would learn to travel to the village to refine it, whether they pay someone to do it or perform the task themselves. They can then go back to the ceremony with the gem. Letting players know through roleplay and exploration that the towns mayor went missing, or that a goblin tribe has moved into an old mineshaft provides them with a reason to go back to that place or to stay there longer and create bonds with it. 

Hope this helped. 

TL;DR - Pick a resource or reason for the settlement to exist (usually some form of resource), then either remove that resource or add outside interference. Finally, add time.

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So, this is where real-life travel and experience can massively help. Settlements in the real world develop around something. Taking the UK as an example, the town of Rhyl in its day was a tourist trap hotspot. Full of life and the perfect getaway for people from cities. It now stands as an all but gutted and hollow shell of its former self. Blackpool is not dissimilar in its state of disrepair. 

Whitby grew up and developed as a fishing town largely to supply the monsatic orders. Therefore it has huge numbers of fish and chip shops.

Parkgate in Wirral lays along the River Dee and once was the bigger and more important port than Liverpool. For this reason there are a huge number of impressive and expensive old buildings. Sadly, the Dee then silted up and made it inaccessible for trade ships. As a result the less preferable river Mersey ended up being utilised and as a result became the major port in the area.

My point here is that settlements grow around something. This something gives the settlement its character. And of course there might be dozens of settlements in an area that grew up around fishing, but even then you can easily have different techniques and processes spring up. Let's take Devon and Cornwall. Culturally, on one side of the border people applied cream to their scones then added jam. On the other side people applied jam first then cream. This small, overegged cutural quirk in the South West of England is a cutural icon almost. No-one really cares, but still when visiting Cornwall with colleagues on tour who had no idea they still wanted to know 'what the right way to put the jam and cream on is'. This leads to the question of why would the people of Devon and Cornwall be the ones to ask about the proper application of Jam and Cream? Well, Devon is well known for its orchards, especially of apple trees. Both are very rural areas with, traditionally, an abundance of milk cows. As a result the market gardens and farms of the area produced staggering quantities of Cream and Jam.

To summarise then, pick a quirk, pick a 'thing' that this settlement developed around. If it's forestry perhaps take a lead from the old stereotypes of the Canadian Lumberjacks.

Once you've got this down you can develop the idea by asking...what would happen with a bit more time. Merthyr Tydfill in South Wales is a good example of this. The entire Welsh Valleys region grew up around Coal, Iron, and Gold mining. In the 1980s coal mining was all but shut down in the UK by a hated British Prime Minister. Nothing replaced the coal mines though and very few could afford or wanted to relocate to where the jobs were. As a result there are huge levels of deprivation and a low general education level combined with low employment levels. Then as time passed immigration and EU investment brought funding to redevelop schools and roads. This one would think would stimulate the area. However, what actually happened was the import of EU workers who already had the relevant skills (as opposed to training up unemployed locals). This was the very simple reason that area voted overwhelmingly for the UK to withdraw from the EU...as one local in that area put it to me 'we can have the best schools and roads in the world, but without jobs and work there's no future for my kids. The money nevers gets to our pockets'. The the Welsh particularly too it seemed to sting that in one particular town in the valleys more Polish was being spoken than English, let alone the native Welsh language. I'll leave readers to interpret how that altered the social dynamic of that particular town.