Had the same problem myself, and looking back I realise I should have just looked for a new job sooner than I did. Although the bosses "really appreciated" what I did they also constantly gave the impression that it would be a struggle to pay the employees if such and such wasn't done by the end of the week. I was also bad at estimating the time for tasks and often found myself overworked because I had underestimated how long something would take.
Project planning is key here. You need to do a planning meeting for each week during which you tell him how much can be accomplished each day. If your boss interrupts you with something urgent, you need to get a definite answer from him on what the highest priority (and don't accept "They're all priorities" as I sometimes mistakenly did, get him to put a number beside each one), state explicitly that this interruption will push out the delivery time of the task that was interrupted.
Never give a range of how long something will take, e.g. 2 to 4 hours. You think you've allowed yourself 4 hours but your boss - himself probably under pressure too - expects it in 2. Just say 4 hours.
Don't tolerate emotional blackmail. I'm guessing your boss is really generous with the "free" rewards (i.e. compliments, understanding and appreciation). Doing a 60 hour week should really be only in exceptional circumstances.
Regarding needy customers, you need to just set their expectations right. They may be needy because your boss has promised them a quick turnaround to improve his sales. If something is going to take a long time or you won't get to look at it for another three weeks, tell them up front. They may get annoyed at that, but they'll have to just put up with it. They'll appreciate it a hell of a lot more than if you promise it the end of this week and fail to deliver because you underestimated or had to do something for another needy customer. Again you need to be assertive.
The question really is, if your boss can't earn enough to pay his employees for an honest week's work, does he have a viable business? If not, you need to look for a new job.
Finally, your boss may talk about how, once it's established, the company is going to be huge and you, having been in on the ground floor, are going to be rich. Don't listen! Maybe it will, maybe it won't. But don't take the gamble based on what he says, no matter how convincing he sounds. I'm not saying it's a trick to keep you loyal, he's probably convinced of it himself. Doesn't mean it's true.