I currently operate a few STRs so have a good understanding of that aspect although they're all located in touristy locations.

I understand if you don't want to do that.

Rehab costs and ARV (After Repair Value) are key parts of evaluating deals, so it’s great that you’re diving into these concepts early.For rehab costs, creating a rough estimate starts with understanding the scope of work and local pricing for materials and labor. 

Yes, you can expand (and SBA has some great options for that), but the basis for a strong expansion is really understanding how the business works.

Trying to understand the strategy for investment properties with next gen configuration from the experienced. tysm in advance.

I understand that rents will go up over time and my mortgage payment will pay down the principal, but it seems like investing the $1.43mil into rental properties and/or a low fee US stock market fund may work out better for me. 

I don't understand - what are they taking 10% of?

I think demand is decent.If you're looking in a flood zone you'll definitely want to understand the FEMA 50% rule.

Some wholesalers over charge and don't understand the market and arv or BRRR.

You don't need to know everything to get started; you need a foundation to build on, and the rest will come through experience and then refining your education.You can build a basic understanding of investing in 3-6 months.