Welcome to Sprint Karting! I’m glad you’re keeping a good attitude and keeping your chin up. I started out just as you did, with an old wreck of a 2002 Tonykart Mitox with a Rok 125 that needed a lot of work. For three years I towed my kart around with my car on a 30-year-old boat trailer (converted to haul karts) and was intimidated by all the big expensive rigs. Soon I learned that my fellow racers really aren’t that scary, and many of them would happily help me out with questions and tuning issues. Make some friends, have some fun.
In terms of tuning, obviously gearing is going to depend heavily on the track and the power curve of the motor but on my old Rok I ran 13-80. I think the guiding principle is you should be hitting the rev limiter at the end of the front straight.
Glad to hear your brakes are better. I had an incident where a fitting blew off and I had no brakes. It was messy.
Regarding your carb issues.. I don’t know a lot about the Tillotsen carbs but the principle is the same. Ask around for a good basic setup (needle position, main jet, emulsion tube, idle jet etc.) and then tune by your pants. I set mine to factory once and it was so rich it barely ran. Also I noticed in your pictures you have a conical air filter on your intake instead of a silencer. I’m not sure that would make a difference but I’d still buy the proper intake silencer.