Absolutely, I had futures in mind as I've never traded forex myself.
Not all strategies have the luxury of waiting in queue and being gamed by faster players, also not all limits are hit and the market might just move away. ES for example has a very big minimum tick especially if you're trading the 5-20 minute time-frame.
There's a thing called strategy diversification and trading multiple uncorrelated instruments (asset diversification). Diversification is as relevant in short term trading as it is in long term trading, you can't build the best equity curve following only one signal.
Yep; thicker markets make limit orders less likely to get filled.