Suzuki Repair: Suzuki questions, suzuki sidekick sport, suzuki sidekick

Question
Hi got a decent bargain on 1998 Suzuki sidekick sport which was a blast to ride last year but its been in the garage since because of insurance money problems. Been in the garage since September of last year ( same oil and gas), any recommendations for service?  Can I use the same gas safely? is it ok to use the 4 wheel drive *(got to go outside and manually put it on).The idle runs a tad fast but not sure if my local mechanic can fix it.  He said its self adjusting and should not mess with it. Do you recommend me taking it to Suzuki dealer instead even though mechanic told me he wants to do all the work.
finally if you don't mind this follow up, there was a slight vibration right under my seat on my way home 100 miles), could that be a transmission even though no skipping of gears yet?  thanks so much

Answer
It's really a fairly easy vehicle to service, let your mechanic do it.  Let your mechanic help you with your concerns, he's near, knows you, and you can get better answers from him, because he can hear and feel the vehicle, all I can do is make a best guess based on my knowledge of my sidekicks(all 89 model year).