"Finally, when you cast a spell with a range of touch, your familiar can deliver the touch. Your familiar must be within 100 feet of you, and it must take a Reaction to deliver the touch when you cast the spell."

How should I interpret this?

Is moving towards the target part of delivering it (just like a mailman would move towards the intended recipient to deliver the mail) or does the familiar already need to be in touch range of the target in order for this to work?

"Is moving towards the target part of delivering it (just like a mailman would move towards the intended recipient to deliver the mail) or does the familiar already need to be in touch range of the target in order for this to work?"

I have always interpreted this to mean that the familiar needs to be within 5 feet in order to touch them, so you need to move the familiar within 5 feet if you wanted to do a touch spell as an attack or if you can cast cure wounds within 5 feet of an ally as an example.  Ideally, the familiar goes in initiative before you do and the creature you want to deliver the touch spell does not go before you do.  On the familiar's turn you move it to be in place, on your turn you cast the touch spell, and the familiar uses it's reaction to deliver it.  

Quote from NienkeF >>

"Finally, when you cast a spell with a range of touch, your familiar can deliver the touch. Your familiar must be within 100 feet of you, and it must take a Reaction to deliver the touch when you cast the spell."

How should I interpret this?

Is moving towards the target part of delivering it (just like a mailman would move towards the intended recipient to deliver the mail) or does the familiar already need to be in touch range of the target in order for this to work?

The familiar needs to already be in range to touch the target. If the familiar were able to move toward the target as part of this, the spell would say that.

DEER FAMILIAR

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Quote from Sennith13 >>

My player is trying to use Pact of the Chain Find Familiar to use magical items. Can Familiars even use items?

Depending on the Familiar (Imp, Sprite, Sphinx of Wonder) if it has the intelligence to do so than yes. But they also have thier own personal so it may not go the way your PC thinks it will go.

So using the senses of the familiar as a bonus action - does this mean you can now attack with your familiar's senses if your character had the blinded condition? 

Is there a way to give it arcana proficiency?

Remembe: when you are looking through the familiar's senses you are more "passenger" than "driver." You can communicate with your familiar and instruct it to do something, but it is still limited by its own intelligence. You can't, for example, go into your owl familiar and try to get it to write a message using its claws. Well you can try but getting it to understand can carry out your instructions would be nigh-impossible.

I don't think they can. Mimicking a sound is not the same as saying a word. Intent matters. 

HailRobonia's Home for Retired Familiars

Honestly they should have made familiars a generic/"templateable" creature. Select xyx options when you create it, and perhaps casting it at higher levels gives small additional abilities and increases HP slightly.

That way there are familiars other than owls and various "uh oh did this new CR 0 beast just become an overpowered familiar?" situations.

Yeah. It's not an "attack" action.

The way I usually see it is that this is really fine incense, created precisely for enchanting purposes, so it makes sense that a small quantity would cost that much. Similar thing with parchment to transcribe spells with, it is fancier therefore it costs more

Can the familiar be used to flank an enemy? Or be an ally for a rogue´s sneak attack?

Absolutely! Can even take the "help" action to give advantage too..

Quote from Drumgirl94 >>

Can the familiar be used to flank an enemy? Or be an ally for a rogue´s sneak attack?

Flanking isn't a thing in this version of D&D, but it can certainly be used to support Sneak Attack or any other feature that requires an ally to be positioned somewhere in particular.

As FrankyDotExe pointed out, familiars can also take the Help action to provide advantage on your (or another ally's) attack. This sort of thing is particularly useful with the Owl form, since its Flyby trait allows it to fly away from enemies without provoking opportunity attacks.

The newly published familiars for the Crooked Moon supplements are all CR 1 creatures. I haven't found an in module reason behind it. Are these now available for everyone who has the spell?

Quote from Nechaef >>

The newly published familiars for the Crooked Moon supplements are all CR 1 creatures. I haven't found an in module reason behind it. Are these now available for everyone who has the spell?

Certainly not by default. It's up to your DM whether any particular third-party content is allowed to be used in your game; check with them.

I don't own Crooked Moon, but it's possible they're intended to be used with the Warlock "Pact of the Chain" feature, which already offers several specific additional familiar options that override the CR limit.

Possible, but it's not mentioned.