This applies to both the fuselage and finish kit. If you are putting in a park brake, matco parking brake is worth ordering, plus delete the existing brake lines, as they won't fit when you have the park brake in place and you will need to fabricate some new lines. Ordering firewall and belly fire protection now is worth considering (titaniumgoat.com for titanium, McMaster Carr for stainless foil and Aircraft Spruce for fiberfrax or use and equivalent biosoluble material like Morgan Superwool HT). Along those lines, you may also want to delete the 2" heater vent, as this is aluminium and an alternate stainless version is available online. You may want to order choose to delete your master solenoid and order the low draw Blue Seas solenoid to that you can get the arrangement right on the firewall to rivet on doublers, and perhaps even the battery box from EarthX if you are going down that path (and subsequently delete the PC680 box from Van's which weighs almost the same amount as the entire EarthX battery). If you operate off grass, then you may want to look at a tire delete and ordering the 380/150x15 for one inch extra diameter and width (but will still fit in the regular wheel pants). The Van's cockpit vent kit is also a little rough and ready, so you may want to order some fancy vents from Stein or equivalent, as fitting these early is a good idea as you may have to make longer flanges to interface with the fuselage skin. You'll still need the Van's vent kit as it contains all the tube, NACA ducts and hose clamps you will still use. If you are going with an Andair fuel pump, get that early so you can fabricated the mounting position in the center tunnel. Just make sure you get allow plenty of room for the bends and flaring in the lines, as these take far more room than you will expect if you haven't flared or bent lines below. I didn't and I had to re do my pump installation. Where you are going to place your fuel filter/gascolator is another one to think about. Most pump manufacturers require these upstream of the pump, so I put one in each wing root, so this is another thing to be thinking earlier than later.
That's about all I can think of for now.
Good luck.
Tom.