CM,
You have been "lurking" for quite some time haven't you?
Let's just start with some general ideas/questions before we get full blown on a trailer.
First, photos are needed. You should get pics looking from the bow and stern as well as at least one from the side. This will show how the hull currently sits on the trailer (too long or short),how the bow eye meets the front brace, the winch location, and the type (roller or bunk). The rear shot will help determine the bunk/roller placement in relation to the stringer system. Let's start with that.
Tires can be deceiving. They look new because they have deep tread and show little wear? UV radiation is the biggest killer of trailer tires so get a couple of pics aimed right at the tires. What about the rims???
Hubs. They need to, at the very least, be repacked with the proper wheel bearing grease. When doing this, the bearings and accompanying race surfaces need to be inspected for any signs of wear /discoloration. A competent shop will do this and replace as needed. Since the trailer is new to you, you want to establish a baseline of maintenance and go from there. Starting fresh with new bearings and seals tells you exactly where the last maintenance was done. Replacement may not be necessary and cost is always a factor but knowing what you have is important when you consider, wheel bearing failure probably occurs more often than a flat tire.
Don't forget the lights.
Lastly, it may be in your best interest to replace the current trail with a proper fitting one (long run cost may be equal or less) but again, pics will help.
Post up some pics of both the trailer and boat. We have a few trailer fanatics here to help.
Good luck.