Your situation sounds 'marginally' similar to mine. We have lived on a farm for the past 25 years. Over time, space issues have expanded as my interests have progressed from maintenance on my equipment and vehicles, to street rods, and now into machining. I learned many years ago, NEVER get rid of tooling or machines. You almost always immediately regret it and, in my experience, it's not out of the realm of likelihood you'll end up re-purchasing it in the future. So if your circumstances allow it, go for the space.
We had a 24 x 48 pole barn with a dirt floor that I ended up converting into a shop. A few years later, I put a 16 x 24 addition on the back which is now exclusively the machine shop area. I've never looked back on those modifications, other than wishing I'd made the addition larger.
If you decide to build the garage, and based on experience, I'll offer two suggestions. First, if your terrain allows it, put a pit in one bay. I do all my oil changes and quite a bit of maintenance work over mine. It makes life much easier than crawling under equipment, and you'd be surprised how handy it will be for other applications. If you do that, make sure you stub in air for impact tools and electricity for lighting and electrical tools. Second, if you can manage it, make the ceiling clearance over another bay tall enough to add a lift. Just like the pit, it facilitates maintenance and other, more challenging, repairs. If you allow for height clearance, MAKE SURE you also allow for foundation integrity. My recollection is that for passenger vehicles and light duty trucks, you need a six inch concrete base (probably 3,000 wt. concrete, but that's a bit of a guess). Lifts are not nearly as expensive as you may think. I don't remember the orders of magnitude, but I was surprised at how affordable they were after seeing one in a friend's shop.
I've done both, and I can tell you from experience - they're well-worth the investment. Especially as you get older. There's no way I could continue to do the crawling around, over and under equipment that I did ten years ago. And like they say, you can't take it with you.
Regards,
Terry