Work through the examples you can find, and get either/both working…
Then, as you try to stitch it together, bring your code, and we can offer further suggestions.
A good starting point would be a block diagram, think about your power supplies etc, then a schematic and basic code (no fritzing drawings please)
I’m sure we can help you make good decisions along the way.
BTW SIM800 won’t be much use by the time you finish this project, it’s only 2G compatible.
If you’re a beginner, I can see this easily taking several months to get it ‘right’.