I guess by FX trading you mean “many positions on currency pairs that I do not intend to keep open more than 6 months” => This would break one the criteria that tax office uses to decide if you are a “professional” or not. if they deem you professional, then all of your capital gains (including your mustachian investments in ETFs) will be considered as taxable income, and thus taxed at your marginal tax rate…
I don’t think it is worth the IB fee allowance… 