If you see 80mph forehands flying around the court, I must first note that it's starting to be a bit scary, although putting that 80mph forehand in a suitable target will prove to be a real challenge for the vast majority of recreational players -- that is, assuming they do hit that hard at times. Most people can't hit hard and remain passably accurate, unless they're fed balls at the right pace in their wheelhouse, so they'll hit big right into the hands of their opponent... And fast balls right into the hands of any good player means a very good shot will come back... So, yeah: hitting hard isn't everything. You should hit just hard enough to be annoying for your opponent -- i.e., if he doesn't get easily forward and can't control points too easily, it's good enough.
As for variety, it's not that important at all. The vast majority of people will vary their choices too much to mimic a genuinely random selection process and will adopt certain patterns without noticing. You can't really fool a good opponent with that and, if he's not that good, you probably do not need to fool him all that much. Even if you know you're going to strike a return off an out wide serve, if the serve is good, you're still going to make contact way out of position... no need to do much more.
What is important, however, is to select an appropriate degree of difficulty in trying to annoy your opponent. Hitting harder, take balls off the air or on the rise, etc. are all ways to take time away from your opponent -- which can be valuable. It also happens to be the set of decisions that are the toughest, most technically demanding to implement. You need a much, much better forehand to be able to hit on the rise or strike a drive volley so that you catch your opponent out of position more easily than it would to change direction more often to make the same opponent run more. If you want a good rule of thumb, try to limiting your mistakes (go cross-court almost all the time, for instance) or playing more balls into your opponent's weakest wing before forcing them to run and trying to take time away from them. Most amateurs will have trouble with these two simple guidelines and it will have the advantage of being way easier to make happen for you.