So with that said, more questions.
1. Using a 1500 watt inverter, what size cables should I use for a 12V system. Then what should I switch them out for for a 24V system (if needed since I will most likely need the larger gauge for the 12V)?
1500 watts / .85 conversion efficiency / 12 volts low cutoff = ~147 dc amps
~147 dc amps / .8 fuse headroom = ~184 fuse amps.
2 awg wire rated for 105C will get the job done.
But who wants their wires getting hotter than boiling water.
2/0 awg will stay under 90C.
BTW that is out of spec high for your overkill bms.
2. Will my 15 Amp Victron Blue Smart Charger be acceptable for the 12v version of the system until I convert it to 24v?
How many amp hours is your pack?
Ideally you want to shoot for a charge rate of .2 to .5c.
Charging at 15amps isn't that terrible though.
The other factor is how configurable is the charger?
3. What do you suggest I use to monitor the SOC to know when it hits 50%? I know I could use the BMS with the app, but does anyone suggest a specific easily visible meter or something I can put on it? I know Victron has their smart shunt too.
You overkill bms does current accounting.
If you want a discrete meter get a shunt based battery monitor.
Victron is the Caddilac, Aili is the Chevy.
4. I would like the charge and 50% cutt-off to be automated if possible so I don't have to mess with the system. Even if that means going with something more like an all-in-one system. Suggestions are welcome.
You do this by setting the charge voltage based on observing the shunt and seeing what charge voltage correlates with 50% charge.
Hopefully your charger does sensible charge termination.
To figure out what 50% is you need to figure out what 0% is and what 100% is.
You do this by fully cycling the battery.
You need to top balance first before you can fully cycle your battery.