Opinions are going to differ, on that one, I think.
But that’s probably part of what makes it a good question. 
The problem with having only one is that if (some people would say “when”?!) it stops working, you’ll be back to square one. And I think that’s quite a strong argument, really.
But you’re definitely right that at the start multiple strategies are too much to handle.
IMO you can’t go far wrong sticking to trend-following trading, whatever stage you’re at.
But understand clearly that trend-following doesn’t necessarily have to involve trend-lines (though it can).
“Supply” and “demand” are HUGELY misunderstood in the context of forex trading, and you’ll benefit (at least for now, and maybe for longer) by ignoring them.
Support and resistance, yes, definitely.
Supply and demand, that’s a big NO. Terribly misleading.
Remember, with CFD’s you’re not trading, per se: you’re betting against a counterparty. Your “broker” isn’t actually a broker at all.