Also with Apple moving to ther own silicon chips will the intel Macs become obsolete quicker? Or will they last for at least 10 years or so?
If you need any Intel specific features then stick with that. However if you can get by with Rosetta 2 then it's best to wait and go an ASi Mac. The Intel Macs will be good for 10 years but they'll be running off legacy apps by that point. Older Macs can stll be very useful if you don't need the latest versions of things or bleeding edge tech.
My current daily driver is a 2011 iMac and it's still serving me well today. However I am in the market for an ASi Mac.
If you own an older Mac I'd check which (if any) 32 bit apps you rely on. As those will not transition over to any modern Mac as they are all 64 bit only.