Welcome to the kart world! While I don’t know anything about the specific model you bought I will throw some info out there to hopefully help you along.
1) Do you know what class you are planning to run? You posted in the shifter kart forum and mention a “125”. This leads me to believe you have a 125cc shifter kart package. Is this correct? If so, what brand of motor do you have? The most popular is the stock Honda 125cc but there are several other 125cc motors out there.
2) When you say “rear dual caliper brakes” do you mean you have two calipers on the rear rotor? I believe this was common to satisfy a dual braking system requirement in certain organizations. SKUSA is one of the big names when it comes to shifter karts and they require 4 wheel braking which means you need to have 3 calipers (1 for each front wheel and 1 for the rear axle).
3) The kart itself doesn’t require much maintenance. The only item that I would consider requires monitoring and maintenance are the rear axle bearings. Some people like to wash them out with brake cleaner and apply a light lubricant (Tri-Flow is a popular name) every outing, while others won’t touch them so as not to introduce any dirt and debris into the system. Either way works, it’s just what makes you more comfortable. Personally I run SKF bearings and pull them out every 3-6 months and clean them really good (they are serviceable unlike most kart axle bearing) and apply a heavy grease. I don’t do anything else to them.
4) The motor maintenance is the most work but it depends on what you have. Give us some more details so we can help.