A Steam copy of MW2 is the preferred way to play ♥♥♥♥, although it is not the only version that will work with ♥♥♥♥.

♥♥♥♥ is completely external to Steam and Steam Servers and it is impossible to get VAC banned. ♥♥♥♥ players only play with other ♥♥♥♥ players as the servers are completely separate from Steam. You are at no risk of receiving a VAC ban.

Your Steam rank and stats will not carry over to ♥♥♥♥, so you will have a separate rank, classes, title etc. When, and if, you go back to Steam MW2 you will still have the same rank you had before.

You can always manually set your rank back to the level you were if you wish, or use the unlock all button in the barracks menu to get 10th prestige level 70 with everything unlocked.

All information taken from ♥♥♥♥ FAQ[xlabs.dev].