If I was to create my own ERC20 token, would I be able to change my token supply down the line? What other solutions let me adjust token supply if ERC20 isn't an option?
It's your contract so you can write it to do what you like.
Some contracts have the ability for designated senders to issue tokens and send them to an address; Usually this will simply be a question of checking that the sender is on the permitted list, crediting the recipient's account as you would in a normal transfer, then increasing the
totalSupply variable to reflect the new total supply.
However, if you are doing this anyone using your token will need to be aware that you have this power, so they will need to trust you to exercise it honestly. You may also want to look at different forms of governance; For example, you may require the vote of a majority of the current holders to issue new tokens.