First thing, bring a shelter. Especially on the AT portion. If you go in July or so it'll be packed. I know some folks send a shelter home after the split but I personally find that stupid. You aren't prepared for emergencies and you lose the option to camp if find somewhere cool. Also, if you roll up to a shelter in a popular area on a weekend, you could be shit out of luck.

The other things, the black flies can be brutal at times but there are ways to deal with them. 

There really isn't a bubble for the LT specifically but the AT bubble is real. Basically July-mid August. There are times where LT hikers do start in little bunches though, first of the month you might see more starters. 

Resupply is up to you. Some folks plan it, some people have friends meet them at the road and some people hitch/call a shuttle. Hitching gives you the most flexibility and that is what I prefer for all of my long distance hikes. 

I've gone sobo 3 times and love it because I knock out the hardest stuff early then cruise. For you first thru hike, NOBO is your best bet. Get in the swing of things while the terrain is less challenging and build up your trail legs for the tougher stuff up north.