Wow! Nobody has replied to this one.
I'll take it. Welcome to the forums btw!
1. I don't know if they come factory. Try and find your sticker options and it should be there. Yes, the dealer has to activate the alarm if it is equiped. Or, go to your dealer and have them give you a history of the car and it should be at the top what options you have available to the car.
2. Yes, satelite radio is compatible. Doesn't matter what you want it is. Sirius works with the headunit....stations, songs, etc. But if you want XM, you have to get a different headunit and hook it up. I've seen it on LOTS of e46s. You could hide the XM antenna inside your car on the dash...at the front in the middle...looks cheezy but this is from my experience. OR the XM and Sirius antennas are small circular magnetic recievers...and uaually put at the rear of the vehicle near the trunk...usually in the middle.
3. I don't know about which way is best, but if you go to Escorts website it talks about hardwiring your X50 to your vehicle. You have to get a modual to connect to the power supply to your headunit and then you're good to go. Converitbles aren't any different than Coupes or Seadans....
I think I was vague on #3, but maybe somebody else will chime in.