I don't think a Boatsafe heater will adequately protect all of your boat. That's the problem. I don't even think that leaving the 1000w block heaters on ALL the time (which you wouldn't do, anyway) would protect your boat. Even heating the interior of the boat to fifty degrees ALL the time doesn't necessarily protect you in a hard freeze. Even with the power on, the boat can get cold enough to freeze water lines and then they will burst. And some of them are hard to get to.
I taught myself how to winterize my boat. I have had exactly one problem over the years- a burst water line caused by my not getting all the water out of the freshwater inlet line, where I connect to dock water. I didn't use a big enough air compressor.
Here's what I would suggest: pay someone to winterize your boat, but WATCH them do it and take photos if you think you can't remember how to do it all. BoatUS publishes winterizing instructions, and there are plenty of books on engine care that will guide you also.
By systems (this is only what I do- other people, many of whom are far more expert than I am, will have advice as good or better on how to do this):
Freshwater: Run the tank dry. Drain the water heater and bypass it. Use an air compressor to blow all the lines out. If you have two freshwater inlets, you will need to do them both. Put pink antifreeze in the water tank and run it through to all faucets, showers, outlets etc.
Heads etc: I don't know what your boat has- maybe GMs? I don't know much about them, but essentially what you do is empty the treatment systems, and then Tee into the toilet water supply lines and flush pink AF through all the lines and the toilets themselves. Including the treatment systems, whatever they are.
AC systems: You can either drain the seawater sides of all the systems, or flush pink AF through them. Mine drain by gravity. I shut the sea cock off, and drain the system by opening the drain plug to the seawater strainer. That drains the entire seawater circuit by gravity. Other people flush pink AF through the system; I used to do that on mine, but since I can drain it dry by gravity I don't anymore.
Bilge pumps: I have one Jabsco diaphragm pump which I flush with pink AF. The rest are centrifugal pumps which don't need winterizing as the boat is out of the water with the bilge drain plug pulled.
Generator: since you are only winterizing the engine, it's similar to doing the drive engines.
Other things: since it gets cold in the boat, leaving all the lockers open, and having a fan running in the boat is useful. Those low-wattage heat sticks are useful- if you wanted to put Boatsafe heaters in to keep the damp at bay, that's good, too. Covering the engine room air intakes is essential. You might even invest in a set of oil pan heaters just for winter use. About 250-500 watts per engine ought to be enough. (Wolverine heaters, they are very reliable and work great)
The first year you do this is by FAR the most difficult. That's when you have to figure out what works best for your boat. Fortunately there are a lot of 53MYs around with the same equipment as yours, so you aren't along on this. And I suspect you've tackled more difficult projects than this. You should be able to get through it in a weekend, I would think.
And DON'T buy your pink AF at WM. They charge more than anyone else does. Get it at the hardware store- this will involve a few runs to Ace, I imagine. It takes me about 12-15 gallons to do my boat, but yours is much larger and it will take more. Regardless, it is very cheap insurance when you begin looking at replacing things like engines, heat exchangers, etc. Or the trouble of finding ruptured copper pipes in a forty-year old boat, leaking in places you can't get to without sawing a hole in something.
One more suggestion: if you are not living on the boat, you can divide this up into a series of problems, instead of trying to do it all at once. It is unlikely we will get a hard freeze before December at the earliest, so if you started this month, and worked on it one system at a time, you could learn as you go and by the end of the season have everything done and photos etc to show you how to do it next year, if you want to do it all yourself.