So, what I'd look at is the cost of opening and closing the channel, and contrast that to what fees you think you can set. The more you fund the channel you open with the less fees you can charge while aiming to break even. If your channel isn't used a lot, your channel may be closed as soon as your remote has a large enough amount of sats on their side that they judge could be used better (unless you have some agreement). So, you might perhaps estimate that only half of your liquidity will be pushed out. Fiat price has not much to do with anything here. That only comes into play when you want incoming liquidity for receiving payments for something you sell.