Depends on the kit. Sometimes a 'brushless upgrade' includes more than just the motor and esc. It might be worth a few extra bucks.
Other times, you pay a premuim for sub-par rtr electronics that WILL break quickly. In that case, better to buy a kit and build it with your own electronics.
What surfaces are you running on? That would be how I would pick between 2 and 4wd.
I like 4x4 because its fast and generally can go some places that 2wd can get to or run on. 4x4 is more expensive too tho.
Buy the VERY best chassis that you can afford. Buy the best CHASSIS even if it doesn't have all the upgrades you want. You have plenty of time ti upgrade once you own it.
Don't agonize too much over your choices.
Pretty much everyone I know in thus hobby started off with an idea that ONE car would be all they would want/need.
After some time spent on that car, it sort if takes on a personality. It will excell in some times, others not so great.
So.... back to the hobhy store for another buggy!
This is unlikely to be the last RC you'll buy so have fun and enjoy it, and then the next and the one after that!