I'm getting my cdl next year, is it better to have experience driving a bigger vehicle before i get my cdl? I'm getting my class a cdl?

I'm going to get a job driving a ford f450 dump truck hauling an excavator on a 20ft equipment trailer… I believe that if i have experience driving a bigger vehicle w/ or w/o a trailer will help, is this true

Not necessarily. An F-450 isn't any bigger than a standard "full sized" pickup truck, so driving a bigger truck wouldn't really help. But you ARE going to need some experience in driving a truck and towing a trailer before you can pass your road test. The CDL-A road test requires you to back up and park with a trailer attached, and THAT requires practice.

Not really. Each vehicle is unique