I'd suggest going with the large for sure. Buy one at an eggfest if you can to save some $$$. IIR eggs by the bay participates in the SFO eggfest. When it come to accessories skip the BBQ Guru at least until you get familiar with the BGE. A lot of people buy controllers way too soon and they really don't need them.
Charcoal varies quite a lot and the data base at the NakedWhiz is awesome. Sadly Wally World has cut the RO bags down in size and jacked the price so it's not much of a deal buying Royal Oak at Wally World any more. My last four bags have been loaded with small pieces and dust as well. BGE branded Royal Oak is now a lot more competitive on the pricing with the WW price hike and it's really more like a premium Royal Oak as you don't get a bag of dust and bits.
For lighting I buy fireplace lighter squares at TSC. I grab big boxes of them in the fireplace section every year when they put them on spring clearance. Saves a bunch of $$ and they work like a charm.
I spent over 30 years in professional kitchens and IMO the BGE may be the single best cooking tool for a home cook that I've ever seen.
Buy one and never look back.