Good morning sirs. Im a backend java dev and ive been working in investment banks for the last 5 years. Although, i work with traditional APIs for fixed income, not stocks or algo trade.
I wanted to try making some bots just for fun. Im not even interested in making a citadel tier c++ bot that can make me rich and quit my job, just seems a good challenge for my technical skills.

Any tips for starting? Just use chatgpt to create the architecture outline? Also where to get the data? Which exchanges allow me to trade via API? The exchange im using right now doesnt allow it.
At my job they have bloomberg and usa govt data feeds for bonds, i know i cannot access that at home.
How much it costs to run a trading bot? Like data feed subscription + whatever exchange allow api trading?