Regarding your hubs. They shouldn't need replacing unless damaged. Bearings and seals however are cheap insurance. If you have ever had a trailer wheel lock up on the road, you'd make darn sure it didn't happen again.(roadside repairs are tough because seized bearings usually need to be cut off with a torch). Measure your spindle diameter or get the number off the bearing before buying bearings. Same for the seals. 1" and 1 1/16" spindles are pretty common for smaller boat trailers. Bearing Buddies or equivalent are a good idea as well, just don't overload the hubs with grease and blow out the seals.
There is no magic involved with leaf springs, if they look OK they probably are. Pay attention to the bushings in the eyelets. It's not an emergency if they are beginning to crack, but if pieces are falling out, things are gonna get noisy and maybe loosy goosy.
Safety chains are very important, make sure they are sized appropriately and in good condition. Pay attention to the mounting points, they should be attached with proper sized bolts. I've seen them just tack welded on the trailer, which is a no-go. I've heard several stories of the trailer detaching and the welded chains popping right off, bye bye trailer.
