1) It's always wise to drift in a clean area. All the vids you see on Youtube where they are doing amazing drifts are ALWAYS done on clean surfaces. The dirt and grime is kept to a minimum, and clean up is easier, and less frequent.

2) The only way to clean an RC chassis is to disassemble it to a certain point, so that you can also perform maintenance on it, at the same time. It's why most accomplished drifters always build their chassis from kits. They know their chassis inside and out, because they built it.

3) If parts are binding or otherwise not operating smoothly, disassembly, and thorough cleaning with solvents and rags (compressed air is NOT enough) and re-lubing is in order. making sure, when re-assembling, that parts aren't dripping lube is well-advised (they should be lubed, but dry to the touch).

As for option parts, it's up to you, how far you want to go, but consider that if you want to "upgrade" to a better/smoother/more advanced chassis, it would be better to save for that, rather than spend $$$$$$ on a chassis you will eventually outgrow. The Madspeed is an entry-level chassis, and many RC drifters just upgrade to a more advanced chassis.

Yes, a faster servo would definitely help your drifting, and it doesn't matter what company you get it from, just make sure it's digital, and has a transit speed of .10 or faster. The faster, the better.

A front spool is not as efficient as a front one-way, and though the chassis will still have brakes and reverse with a spool, tire wear will also be a concern, and then there is "chatter" when cornering (which is also where the tire wear comes from), which actually slows the chassis as it enters a corner, regardless of how much brake used. The front one-way drives both front wheels independently, so there is no "chatter," and no scrubbing of speed, in corners. The spool is only good, in the rear end, on a drifter.
For drift, a front one-way IMPROVES drift manners of the chassis it's mounted in, and as a seasoned drifter (been at it for going on eight years...), I don't buy a chassis, unless it has a one-way available for it. If the chassis is CS'ed, it almost REQUIRES a front one-way.

On adjustments, that's up to the chassis. When refining a chassis to drift well, it's not what the driver wants, but what works for the chassis. I have chassis that work best with "0" camber, no toe, soft front springs, stiff rear springs, and yet, I have others with adjustments that required certain option parts to obtain them, like 10 degrees caster, and carbon shock towers with more mounting positions to refine suspension settings, among others.