Hey Champ,
Firstly good choice :-)
Show me some pictures of these nuts under the door hinge bolts.
Standard airbox will be pretty easy to come by once you place a wanted add in the for sale section, im suresomeone would love to trade a carton for some spare space on the shelf in the shed. HOWEVER you must remember if you plan to run a FMIC with the stock airbox youll need to run one with same side cold air return or if the cold pipe does come across the engine your going to need to hack up the snorkel. Food for thought.
Post a pic of this grill, i want to have a laugh haha. Neithr of those grills will fit as they are for series 1 stageas and this car is a series 2. Why not wait for a S2 NA grille to come up for sale like this :
Door seals you will be able to get from someone wrecking a stag at the moment.
As far as exhaust goes get a 3inch bellmouth front dump pipe for under 200 off the forums or just jap, then a 3" highflow cat and then go to a local exhaust shop for a 3" cat back with whatever muffler you like ect... OR buy a r32gtr cat back and have them add 2 or 3 sections into it and mount it up.
$12k seems fair. Does it have factory xenons? Floor mats? Boot Mat any other accessories?
Those strut towers look VERY suss IMO. That chaulk is nothing like what it should be from the factory. It is a common rust spot, the question to be asking is has it been "repaired" or covered up.....
What other bits does the car have? Clearly has coilovers.