yes it is fine but of course synthetic is the best to use if you can. Double check your oil requirements with your owner's manual. If it states that normal oil is okay, then go ahead. If your owner's manual dictates Synthetics, then DO NOT switch.
i'd say its better. you might get leaks, because regular oil has bigger molecules than symthetic. i run synthetic in my truck with 193,000 miles all the time no trouble
That's okay.
Yes, you can even mix them.
Yes, you can even mix them.
Yes, and you can even mix them together.
yes
No, you can even mix synthetic with conventional oil. It will do no harm at all.
No it is fine to switch back to regular oil.
It's okay to use Synthetic oil on any vehicle but bare in mind, if your vehicle has previously run on regular oil you will need to drain all the oil out completely in order to switch to synthetic, once you run on synthetic oil though you have to keep the oil synthetic because switching between different types of oil will really mess up your vehicle.
yes, if the car manufacturer dictates that regular oil is acceptable. If your car requires synthetic oil as dictated by your owner's manual, then DO NOT use regular oil. May void warranties if your car is still covered.
If you have kept regular oil changes, no prep is required. Just go and put the synthetic oil in.