Re: Proper HU SNG PF ranges
I think one way of looking at it is:
You want to raise as many BTNs as you can get away with before/unless villain adjusts. So theoretically you can start off by opening 100% and seeing how villain responds. Some people will start off at 85-90%, because opening 100% has a certain feel to it that causes some villains to play back faster ('omg he's blindly clicking raise every time he has the BTN') than if you occasionally fold your BTN ('oh he has some standards, even if they're minimal.')
You may want to start reducing your BTN opens if villain starts 3-betting a lot and is hyper-aggro in 3-bet pots / doesn't fold easily to positional pressure and is generally hyper-aggro OOP / will pay you off lightly but will not go away often enough when you have air unless you put stacks into play every time. In such cases, opening super-wide might still be profitable if you're skilled post-flop, but the match becomes much easier to play if you reduce your opens to like 60%-75%, especially since most villains of the type I described won't adjust well. (For example, there are hugely losing villains whose basic approach is to try to win every pot, literally, no matter how many chips they risk and almost no matter what kind of resistance you put up. Opening super-wide against them can get really tough if you're not running hot or sick good, because you basically have to show them a hand or bluff for stacks or fold and bleed off chips every time you enter a pot.)
As far as raise-sizing pf goes, I recommend HokieGreg's advice (which I presume is standard) when getting started, until you design a scheme of your own that you prefer for whatever reason. The key is that your pf raise-sizing should take effective stack size into account. You don't want to be opening 3x when too shallow, because it's pretty easy to exploit by 3-bet shoving, unless you open a ridiculously low percentage of hands. There are posts about this on this forum; search for "3-bet shoving 25 bbs deep" by Insane_Steve. Anyway, HokieGreg's advice: raise 3x between 75-51 bbs deep, raise 2.5x between 50-30 bbs deep, and raise 2x between 30-13 bbs deep. Below that, a lot of people start playing push-or-fold preflop, using the Nash Equilibrium tables as a guide.
As far as limping is concerned, some people never/rarely do it, and stick to raise-or-fold pf, and do just fine. Others will limp anything they're not raising, until villain starts attacking their limps, and then they'll mix in some strong hands into their limps and fold the very worst of their limping hands, in order to make life harder for villain. I typically don't limp until the effective stack is less than 23bbs, then I start doing it with many weakish and some strong hands. So there's a lot of flexibility in this arena.
Finally, you say OOP you call anything remotely decent and raise all decent hands to 3 bb. I'm not sure exactly what ranges you mean here, but I strongly recommend starting out by playing very tight OOP. You can call min-raises a little wider than 3x raises, but the key is to play OOP pots much less frequently than pots in position. Look for hands that flop well, where both cards can make a decent pair, so K9s > A2o. Also watch how frequently your opponent raises; you don't want to be calling with dominated hands against a nitty BTN-raiser (they do show up.) Your OOP play is of course conditioned but how well or poorly villain plays post-flop. Some guys will give you free turns when they miss and check/fold when they don't connect and you fire turn or river. Others will c-bet 100% but play very weakly against frequent check-raises. But please, please start off by playing tightly OOP. And if someone limps into your BB, don't raise their limp with a wide range until you know exactly what you're doing. Start off by only raising limps with something like 88+, QJ+, KT+, AT+, and taking free flops with the rest of your hands.