A close-up of the tag on the generator should tell the specs on it. I would guess about 20-25 kW. You need to know what voltage(s) the generator will do. 3 phase or single phase etc.
A manual transfer switch can be had for several hundred bucks from places like Harbor freight on one of their sales.
I really think the price is too high. You could get something a lot newer for a lot less. The other thing is how much load you will be able to apply to it. An old CAT is most likely going to be prone to slobbering unless you can load it up pretty good every now and then throughout the day.