[room217au]

truck order:
By-and-large it doesn’t matter because they are (almost) all independent of each other, and SCS trucks.
However, the K200 and K108 do share some parts. eg. The K200 uses the K108 mirrors. Some textures are common amongst trucks. T609 an T908 share interior textures. All of the above really doesn’t interfere with game operation tho. The only time there might be issues is if you edit any of the models. You might get “unexpected results” at runtime 🙂
quick jobs:
I can’t really say about that because one of the first things I do with any modded truck is remove the “truck_company” folder completely. I don’t do quick jobs unless it’s with SCS trucks on a brand new profile for beta testing purposes.
sounds:
The way it works is that trucks are grouped together for sounds. The sound files re separate so that different trucks can be updated separately. That’s what RTA say anyway 🙂
For each truck you need 3 files: part1, part2 and the sound pack. There are other files too, but we’re just talking about sound for the moment. When you unzip the 7z archive, you’ll notice that some of the trucks have the same sound pack. You only need ONE of each sound pack. For example:
RTA_Sound_Pack_1_v1.2 has sound files for K108, K200, T908 and T609. So for any one, or all, of those four trucks you only need that one sound pack.
Just check where you unpacked the 7z file from your MEGA folder and see which sound pack is included with which truck.
The mod order of trucks and sounds shouldn’t matter either.

To be honest, I do some very heavy editing of any RTA model. Mine are far far from standard and I’ve never used Robinicus’s sounds for RTA trucks. Always Kriechbaum. Always.
Good luck and I’ll try to answer your questions as best I can.