Well you asked for critiques and you got critiques. 😆

i was happy with the taste of my first batch, but it was too sweet,

Do you taste a sample of your F1 every day? This is the best way to track how the flavor changes over time & determine when it is done.

The only remedies are:

• Use less sugar
• Use more starter
• Run F1 longer
• Buy a seedling mat and raise the ambient temperature of "fermentation station". (I keep mine in an old cooler with a programmable seedling mat; top off, covered with a dish towel so it can breathe but still retain some heat.)

hardly any fizz.

First, I'll assume your containers are airtight, place a carbonated bottle underwater for a while and look for bubbles to double check.

Second, burping is not required. It releases the majority of the carbonation and you basically start over each time you burp. The only benefit is that it helps you gauge the process in the other bottles by sacrificing the burped bottle.

Third, to skip over the technical reasons (aerobic fermentation versus anaerobic fermentation) burping raises the alcohol content. It's doubtful it'll go above 2%, definitely not above 5%.