Ok, it sounds like you are not a professional with specific needs, so you have choices but choose wisely.
You can buy an iMac today that is very capable and will last you 5+ years if you are someone who hangs on to things that long. It will do everything you need and more, again I am assuming you have no really specific needs.
Or, if you really want to wait until Apple has put their own chips in the iMac you need to wait until next year, no iMacs with AS are coming this year. But, also consider that 1st gen iMacs with AS are going to have limitations, bugs and issues that you don't really want to deal with as a new user of macOS.