Synthetic oil manufacturers.
Follow the manufactures recommendation or change the oil/filter every 5,000 miles if you use conventional oil or every 7,500 miles if you use synthetic.
Atlantic
Depends on what the manufacture of your vehicle recommends. Can be as little as 3,000 miles to as much as 10,000 miles. Follow the manufactures recommendation.
You can mix part synthetic oil with full synthetic oil.
Semi synthetic or synthetic blend is a combination of synthetic and conventional oil. Full synthetic oil is just that 100% synthetic oil.
Oil that comes out of the ground is not synthetic but is called crude oil. Synthetic oil is man made with synthetic compounds. They are both oil.
Most manufactures recommend SAE 10W30 or 30W. I recommend you use 10W30 Synthetic in any air cooled small engine.
I have an 08 Rubicon. It takes 5w-20w. I switched to full synthetic after my first 500 miles and have had no problems.
Yes, Synthetic oil is synthetic oil no matter who makes it.
Yes, that is what a synthetic blend is that they sell.
It is a combination of synthetic oil and conventional oil.
Synthetic oil is synthetic oil. Any major brand will be of high quality.