Hey, Firstly, to get the yellow taxi lines you need to change the setting in the display option,
Start flight sim, settings, display, and crank them up somewhat more than half way (not sure exactly what ones and how much as I havent played them for a while)
Secondly, The IFR altititude clearences you receive, will be to different flight levels, somewhat like in real life, If you've requested FL
410, you'll be cleared to, FL5, FL120, FL
160 and so on till FL410.
Hope this helps!