Blueprinting is making sure the engine parts are correctly cut and assembled within specs and tolerances to give performance and reliability. Some of it is crank alignment, port timing, CC’ing the head. etc. Some is not worth doing yourself simply due to tooling cost. This in no way diminishes that there is skill and knowledge involved that has value.
Weight is added by bolting on weight.
My suggestion of find a class you can run locally and take it from there. Every class has a downside. Usually it is either cost or performance. Having a full grid probably helps with the fun and learning. Talk to some of the guys in the class you are considering. We run some hard tires so tire cost is good for us in a local spec class. Most of the expense is fuel/oil, race fees and kart upkeep. Upkeep is mainly engine, clutch, chain & sprockets. Local spec classes are great if you just want to stay local. Our tracks configuration changes often so that is a plus for me.
Chassis tuning is the big issue. This is where you will gain & lose most of your speed. Spending a little on some stuff to get the kart to fit you will need to be considered as well as some pit equipment if it doesn’t come with the kart. Chain breaker and clutch tools are specialty tools I needed. Most other tools are basic. Maintenance is a lot of cleaning and checking. Staying on track makes life easier. Leaving the kart at the track can be a pain in terms of accessibility & I live 10 minutes from the track.
The bang for the buck is in karting. I was going wheel to wheel for less than the cost of licensing in a car. Probably $3K to make it to the first race. Some items can be borrowed at first too. The g’s pulled in the kart and the amount of turns is where the karts are fun for me.