I see your location is Ithaca, NY. If you're on spring break and coming from Syracuse...are you an Ithaca College student? I'm an IC alum (Park School) myself.
To answer your questions if you haven't departed yet, 49 vs 449 makes no difference. Likewise, 48 vs. 448 doesn't matter unless you're headed east of Albany. In that case, you'll definitely be in the 448 cars.
Westbound, usually Chicago-bound passengers occupy the last car. If it's not full, they'll likely have you seated in that car. Eastbound, Syracuse-bound passengers are usually in the 448 cars. You don't need to worry about engine/horn noise; the furthest coach car forward is the fifth car in the consist (engine, engine, Boston sleeper, cafe car, first 448 coach).
Around spring break, the trains will probably be sold out, especially on a Friday night.