"Any Phase: Pay 1 gold to choose a HL character. Until the end of the phase, that character gets +1 STR"

There is nothing wrong with paying 3 gold (three actions) and make someone STR +3, right?

I'm 99% sure, but still a beginner, so I prefer to ask.

You're correct. If there were a limitation, it would be printed on the card. If you had 400 gold, you could make a character +400 STR.

Rogue30 said:

The fact that it is three separate actions (giving +1 STR each) is really important, though. Between each +1, your opponent's get a chance to do something. Could be a big deal if you're playing against Targaryen....