It's my very first time playing dnd and i am about to dm a campaign for a party of three(all first time players). I want to concentrate on social interections and wilderness survival, but still make it challenging for them. The problem is I don't really have a feel for the game yet. Are 5 bandits way too much for a 1/2 level party? Is a swarm of wasps a good idea for a random encounter in the woods? Should i give them magic items to balance it out? I'm lost. Any advice would be highly appreciated!!

Edit: the vibe is leaning towards realistic(you are in a big town filled with tourists, your money WILL get stolen if you don't hide it well.) So it should be challenging for three teenagers to get to their destination. But at the same time i dont really want to kill them 

By your description, I'm guessing you are running a homebrew campaign of your own design. While not at all impossible, you've chosen the challenging path first. For first time DMs,  with first time parties I would recommend a learn-as-you-go style adventure akin to Lost Mines of Phandelver. I'll reiterate that this is not a requirement, merely a suggestion for you to consider. I would also, point you to the DMG and Xanathar's Guide for some reference material regarding encounter building and random encounter suggestions, if you have access to them.

• For a first encounter 5 Bandits might be too much for a group that has no experience in winning a fight, or for a DM that doesn't know when, or how, to pull a punch. A more likely matchup would be 2-3 Bandits, or 4-5 Commoners statblocks that you describe as bandits (referred to as: reskinning). 
• A single Wasp Swarm could be a good encounter for a party in a forest, as could a lost child or pet, hunters, loggers, other travelers, a ruined cart, old ruins....anything that might be in an old forest is an encounter. Crossing a river or stream is an encounter, unless you don't want to make it a challenge for the party. 
• Not all encounters *have* to be resolved by combat. If you put a creature infront of the party, allow them to figure out a solution. Regardless of their choices, your job is to play the creature by its personality and interests. If there were a scared child in the forest, and the party runs up to it, it might attempt to run away, thinking the party dangerous with all their warmaking equipment on. If it were a hunter returning with its quarry, they might react cautiously but ultimately, they are more concerned with getting the game back to the table.

Good luck, have fun! Welcome to D&D!

Thank you so much! Yes, I decided to run a homebrew. Mainly cause I'm pretty decent at improvising and after reading some books and blog posts i became a little anxious about making up something on the fly that could mess with things later in the module... Your advice is incredibly helpful! Thank you once again 

One thing you can consider as a baseline is the encounter calculator n the DMG, where you use the XP for monsters to work out how difficult the encounter as a whole is.

Note that most people agree this is a very rough outline and by no means definitive - you might think you're making an easy encounter and it be hard, or (more often) making a deadly one and it be easy. Your mileage will vary based on what the party can do, how offensive they are, and what monsters you pick.

Also, avoid single powerful monsters. They might be the right XP rating, but thye will probably knock 1 PC down to basically no health (or outright kill them), then die to getting mobbed by the rest of the party, because Action economy (how many things each side can do each turn) is important as well.

Have fun! if you're about to accidentally kill a PC, you're only learnign so just say "you have 1HP left" rather than kill them, until you get the measure of it!

Thank you! I thought to maybe throw an owlbear at them but as you pointed out it won't be the besf idea. And the one 1hp thing sounds incredibly useful