Is your garage attached to your house or not? If not I would up the 'R' value on the insulation.
I'm sure there is a man door leading outside? Make sure it's an insulated door with weather stripping and have a door sweep installed because you will a lot of heat loss in that area if you don’t. Also, are there any windows in your garage? Again, another area where there is a lot of heat loss... so you might want to consider either upgrading your windows to HE or make sure that the weather stripping & caulking are checked. I know you can install this film on your windows to make them more efficient, but I don't know much about it. Curtains or blind will reduce the heat loss as well. But if you don’t have any windows, all the better!
Is your garage door insulated? Another area where you lose a lot of heat, consider getting the panels insulated... either with rigid insulation or batt. There are advantages to both as well as disadvantages (Batt insulation can be heavy and your garage door will be a lot harder to open because of the extra weight), but it will be well worth it.
I assume that your garage is unfinished (ie. bare stud walls with no gypsum board)... you say that you are going to insulate, I would also suggest installing gypsum (aka: drywall and sheet rock) as this will improve your 'R' value of your garage. Gypsum doesn't really provide a lot of 'R' value, but it certainly doesn't hurt.
As far as heating goes, as previously mentioned, the ceiling mounted space heaters are good... and if your garage is really well insulated it shouldn't come on nearly as much if it weren't.
Lastly, I would suggest a dehumidifier. Not sure how humid it gets where you live, but it will reduce the water that is in the air that could affect the wood in your pins. Plus another advantage with a dehumidifier is that it actually reduces the heat and makes it much more comfortable in the summer time.
Hope everything turns out the way you like it!