In general, the basic set ups and changes you preform will have similar handling effects regardless of the brand, year, model, wear.
A good old used chassis can still be competitive in the right hands. there is some consensus that different geometries and tube diameters are suited better for some classes than others. and/or different tires. but this varies wildly.
As a general rule the heavier the class the larger the tube diameter used. This is also true for the more horse power so for the Junior classes you see 28mm while the masters and shifters trend to use mostly 32mm but this is not always the case as some will use a contamination of 32/30mm and it changes from model to model year to year.
Don’t get tangled on this yet. Just go get something cheap where you can learn the basics and once you know what you might need you may want to worry about tube diameter, geometry and wear. there are all sorts of discussions about the subject here so if you are bored one day go ahead and get some reading.