With it being a difficult property for an investor to find traditional financing for, how would I go about assigning a realistic valuation for the property if we were to entertain a sale?

Starting with a $100K headstart is more than a enough to buy a new primary home. 

I was planning on building the home in the traditional stick built style in my budget but am wondering if doing prefab may save some money/have other benefits.

It would be a primary residence.

It's going to be more about your confidence in the market that you can afford than anything else, so the primary thing is to look up a few areas you might be able to afford and then look for someone local that can hop on a call to give you an idea about what investing there is like. 

If you have not flipped a home, do not have a rental property, and do not own a primary residence, you may have a hard time getting into lending.

I am just starting my investment journey, so have only used Real Estate Agents to assist with buying and selling my primary residence. 

Front had verticals and more traditional horizontal blinds throughout.

I think I've bought 10 houses (primaries and investments), and I've had that same "Oh crap, my chest hurts, why did I think this was a good idea?"

Based on the tenor of your posts, I've got to ask - do you have your primary residence squared away?