Welcome to the forum, Jacquie!
Best oft-repeated advice I hear is to focus on using the trailer for a while before starting major renovations. Clean it thoroughly, make sure it's roadworthy (lights,
tires, bearings), and get out and camp. Experience will help you prioritize improvements.
Regarding
tires, with trailers we go by age, not appearance or treadwear. There is a date stamped into the rubber on the sidewall (read as WWYY = week, year). If they're more than about 6 years old, time to start over. The usual advice for bearings is 12K miles or once a year. Unless the previous owner can verify that it's been done recently, best to get it done- any garage can do it, doesn't have to be an RV shop ($$$).
Have much fun with your new trailer, and post pictures!