Originally Posted by dostidilse
Now my question:-
Hello dostidilse, welcome to the site.
1)You should have no problem picking up Aircraft with the BC75XLT. You should find out the designated frequencies for your area, and make a scan list, that will help you greatly.
2)Yes, a well tuned antenna like Hertzian suggested would work much better in almost all situations, and for portable use.
3+4)If you can get a Yagi, or Ground Plane, or Discone antenna on your roof, you can connect any of these antenna's directly to your scanner, by running coaxial cable (RG-6 at least, LMR / 50 ohm types would be better) down from the antenna and hooking it to the Scanner antenna mount with a BNC connector on the cable.
I would suggest a Ground Plane or Discone antenna to start, because they will receive in any direction which is typically better for air traffic that goes over head, where as the Yagi would only receive in one general direction, which would be less beneficial depending on your situation.
I'm not sure what you meant about a "Booster" but, once you have an antenna and coaxial cable run, you could ad an Amplifier, if needed, to "boost" your signal, and push it down the coaxial cable to your scanner, but try things out without an amplifier first, and determine if you really need one or not. There would not be 2 antenna's involved in the process, which is what I think you were suggesting.
Hope this helps.