1st gear growl and other issues

[dr7966]

99 6 spd coupe with 80k miles bought in Dec 07 with modified exhaust (headers) and intake (K&N).

Has a slight growl or gravely sound only in 1st. Most noticeable at a steady speed. Replaced the blue trans oil with Mobil 1 75w90 and it got a little better. Also slightly hard to get into 1st when cold and the 2nd gear syncro is not 100%. All the other gears shift smooth and quiet. I have owned other cars that had trans noises that were there for years. With normal driving will this keep working for awhile or lock up on the freeway?

Starter is slow when engine is hot and sometimes will engage for a second and stop. So far it has started on the 1st or 2nd retry. I am going to order a new one to be ready. Can the car be push started if the started goes belly up?

Only got one key with the car. It is a one button remote with the electronics and battery missing. Can I buy another key and have it programmed to the car and keep the original as a spare. Can the ECU recognize 2 immobilizer codes?

The radio is a CR-210 with a 6cd changer in the trunk and speakers in the dash, doors, and rear. CD's sound pretty good but the radio (AM and FM) is noisy and changes from bad to worse and back again. The drivers door speaker works with the CD but not with the radio. Is there a fix or should I just get a HD radio?

Engine runs great but uses oil at ~ 1 quart per 1k miles. No leaks, no visible oil smoke. Running Mobile 1 10w30. I dont think the car was babied or well maintained by the previous owners and I have a habit of going up to the canyons and giving it a workout. Are there any recommendations for higher mileage engines? Go to a heavier oil or just add?