Welcome,
Your speed will depend on your wood working skills and the base the trailer base. My first trailer was basically a box. no kitchen the only curve I had was the font top. I had very little skills and it took me for ever to find the base.
If you are using a used trailer, mine was a boat trailer, inspect it and fix it for any rust or damage before you start. On my first big run I was 2 states over and my axel mount broke, 5 years after that the tung broke each time I had to find someone to weld it. But it you have welding skills and a place where you can buy a axel and wheels or kit. There are many plans out there for such. You want 2 doors so you are not climbing over the other person in the middle of the night. The more complex you make it the longer it will take. You can always change it later. My first trailer had 2 door only one had a window and it was not glass but a small board to lift up before I went outside. several years later I made doors for it each with a window, door handles and proper locks.
The People on this forum can help you with any questions you have.
remember make it simple unless you make cabinets for a living. My second one was planned to be a 3 month build and I felt I could do it. But I wanted something better and But life got in the way and it has been 5 years now. I still have my old trailer and it can be pulled to an outing if I need.
Once you are done if you have time you can go back and change things or add things. Your main goal is to have a trailer you can sleep in and can safely pull it down the road. Know the laws for trailers both home and where you travel.
Welcome to our forum as you start put it down in Build journal.
Good luck
Ron