Some things that I wish I had known before I started.

Don't underestimate the importance of setup time on a small boat. Sloops have tall masts, which are more effort to build, set up, and store. Gaff / Lug rigged boats have multiple, but smaller spars. Often fitting right inside the boat itself for storage / trailering.

Every Cotter Pin you need to put in place, with a tiny, fiddly split ring takes more time, especially with cold tired hands. (And bring lots of spare cotter pins, in every size, and lots of split rings)

The more open space in a boat, the more water it can take on. Boats with seats which are storage / buoyancy compartments take on a lot less water than simple park bench seats. I may, over the winter refit my seats, it will be a lot of work, but it would give me tremendous extra buoyancy and storage, and massively reduce the amount of water I'd have to bail out in a swamping.

I should have turned the front frame into a bulkhead. The space forward,  is more or less useless to me. It's too far forward to store anything. It's now filled with a GYM ball as buoyancy. With a bulkhead, and an pair of waterproof, lockable access hatches from the deck, it could be used for storage of light, infrequently needed items. And it would still represent a lot of buoyancy.

I should have bought a trailer with room for a winch. Pulling the dolly up onto the trailer is awkward, and when you haul at it, it can come flying forward. A winch would be far more controllable

I should have turned the frame just under the fore deck into a bulkhead, and put in large hatches. Lockable storage !! Dry storage !! More stuff that I could leave on the boat, ready to go, rather than have to keep it in the house/shed. Again, a shorter "time to water"..