1. Wrenches
2. Screwdrivers
3. Socket drivers 1/4, 3/8 and half
I am getting you essentially to work up to buy the biggest Craftsmen set for about $300 you can. They will last a lifetime if treated right. I have STOOD on a socket (in my younger years of course) with an allen bit that I snapped (of course with my lard ass on it) and SEARS was happy to replace the socket bit.
4. Air compressor.
5. Buy the following air tools at Harbor Freight/Northern:
Die grinder (also get rotary file bits for it to use it to shave metal, cutoff tool, air body saw, air blasting chuck), then you can move on to air powered drill, air powered sander, air ratchets, impact wrenches). With air tools, as a hobbiest, do not get hung up on name brands, we use them less than the pros and they last a long time if treated right as well. I view air power as the biggest garage upgrade you can do once you have the essential tools.
6. Tool
oil. Always be kind to your tools and clean them once a year if you don't when you put them away and give them a wipe with some anti-rust stuff.
If you are building a single motor, you will spend in tools alone what it may cost you to pay an engine builder. If you are planning on bulding several, your list is a good start.