Welcome
Hi Nick,
The internet in general is a great resource for RV builders, but it can be almost overwhelming. Hundreds of people log their projects online -- I'm sure you've seen the list of
links at Van's website. You'll find so much input and opinion here on the VAF site alone that you could spend the rest of your life sorting thorugh it all. 'Information management' has become an important builder's skill, right along with deburring and riveting.
I usually search the VAF forum archives for relevant comments before I tackle each major new sub-system, just to see if anyone has encountered a "gotcha" that would be nice to know about.
If you do use this site as a resource, remember to take everything with a grain of salt and consider the source. Don't make rash decisions about the construction of your airplane based on one person's opinion on a website. Just remember that Van's Aircraft, Inc. ought to be the final authority on most of the big "engineering" questions you might have as you're building.
Having said that, there are a lot of smart people here with valuable experience who will be more than happy to make suggestions and give guidance. (Don't forget to give back to the community by providing your own nuggets of knowledge, too!)
As to specific aircraft models, I agree with Pierre that the RV-4 cockpit is pretty snug for larger guys. I've flown both, and the RV-8 just fits me better. The back seat is more comfortable, too, IMHO. If you have a loved one who will be a regular "backseater," this is the time to get that approval. Definitely sit in each model for a while before committing.
Improvements and enhancements? Wow. There are tons. Just off the top of my head, here are a few that people have done to their RV-8s. You could search the site for more information about any of these. This list is definitely
not all-inclusive:
Heated pitot tube
AOA system
Inverted fuel system
Titanium tiedown rings
LED nav lights
Upgraded landing lights
Split flap hinges
Video cameras in vertical stab (and other locations)
Gear tower access covers
Brake pedal access door
Avionics access door in forward bulkhead
Removable floorboards (screws and nutplates)
Angled side panels below instrument panel
Armrests
Andair fuel selector
Smoke system
Upgraded static ports
Upgraded front seat throttle quadrant
Rear seat throttle
Rear seat rudder pedals
Rudder pedal extensions
Integral brake reservoirs on pedals
Baggage door hold-open spring
Flaps-up shutoff system
Bent control stick in front cockpit
Removable rear stick
Infinity control sticks with custom functions
Dimmable LED cockpit lighting
Rear cockpit map light
Rear cockpit power outlet
One-touch flap positioning system
APRS system
Rudder cable exit fairings
Parking brake
Grove aerodynamic landing gear
Fastback fuselage
Aftermarket canopy
Aftermarket hoses, fuel lines, brake lines, etc.
...Plus about a zillion combinations of avionics, electrical system layouts, and other goodies. I could go on and on. (But I won't because I think I just had a seizure...)
My suggestion: Make it your own plane, using your own priorities and budget. You'll enjoy it more in the end. Don't do anything just because someone else is doing it.
Welcome to the community!