Hello,
I am a Swing Trader (couple of dozens trades a month) and i have my account currency in EUR.
I am willing to trade in USD markets, for I am going to buy all these stocks with a base currency in EUR, I am willing to pay for every trade (in and out) a spread fee?
thank you in advance.
Hey. 
Тhere’s no spread markup when trading in Invest/ISA accounts. If you are trading in a CFD account, the spread might vary depending on the market conditions and the instrument’s liquidity.
On a side note, there’s an FX conversion fee of 0.15% when trading with stocks or ETFs in currencies different from your account’s base currency. There’s a piece of additional information in the article here from our Help Centre.