i have some questions here i thought i could use help and advice on

thnx in advance!!)
1. i just got a 99 le camry like two weeks ago... evven though all the engine parts that need routine changing (im talking all filters,belts,bearings,oils,coolants) have been changed. the check engine light is still on .
the mechanic says its because i put lower octane fuel than what it needs (here regular is 95 octane and the higher grade is 98) . but i read the manual and it says 87 ( reasearch grade 91 or higher) octane or higher is required. any body knows whats going on?
otheer than that the car drives like a dream. only once the car shut off on its own while i was filling gas. the rpm jumped around a little first ...then a little knocking and engine shut off on its own, but it started again with no problems. im gonna start putting high grade 98 octane from now on. hopefully that should solve the problem.
2. the car was imported from the states, has 113300 miles on it, the tyres look new but are 2004's michelin x-radials all season tyres (14" with a B temp rating.. considering that the temperature of roads in the middle east are way hotter than usual roads in the states or canada.... is it safe to continue using them?
3. the cd player is a standard toyota kit... and it skips sometimes.... is there any easy routine maintenance i can do for it? or do i need to take it out and service it by professionals? plus how long before the cd player stops playing cds completely because its gotten too old?
if these issues have been dealt with b4, sorry about being such a newbie.... i'll try serching the tons of threads if that is so.