Can't decide between SC or IBKR?

IBKR does come with certain costs due to the inactivity charges. Luckily for you, up till you hit 26, the fee is only USD3 per month (less any comms incurred of course).

However, one thing to note is IBKR's FX rates and comms are light years ahead of SC, which would likely lead to greater savings in terms of overall cost.

As a former SC user, transferring positions from SC to IBKR is quite pricey (USD39 per counter). But if you dont mind it or you're ok with selling it all in SC and buying back in IBKR, starting with SC is fine too.

My advice would be to just start with IBKR, and just keep adding to it. With enough discipline, salary raises and compounding, I would think you should be able to get to your 100k USD in no time (to waive the inactivity charge). All the best!