You could try captrader or lynxtrader instead, which don’t have minimum monthly fees. Under the hood they both use IB’s platform, but charge somewhat higher transaction fees.
In margin account you’ll be able to loan cash from the broker with the collateral of your stocks. It makes things generally a bit more flexible even if you’re not going to use this facility. You could for example first buy a bunch of stocks and then convert currencies to cover exactly the prices you’ve paid. Or buy the dip before you get your next monthly salary or wire transfer arrives at the broker. Or request a withdrawal without waiting several days for a trade to settle. The interests are actually pretty reasonable, 1.5% p.a. for CHF currently.
Which commissions type - Fixed or Tiered?
Tiered is often cheaper, even at small volumes. With fixed IB charges you a relatively high commission to cover worst case scenarios. With tiered you’d pay a smaller commission to IB plus exchange’s commission, which depends on exchange, type of product traded, whether you add or remove liquidity from exchange. Some exchanges (e.g. BYX) even pay you for removing liquidity, so net it can cost less than IB’s commission.