Question 1: Does $4698 for materials and labor to prepare my house for a hot tub seem in line?

No, material costs sit nearly identical.

I was able to negotiate a package that included the land, some of the materials, and the permits to build it.

When you have a big cost segregation depreciation plus your big startup expenses such as furniture and supplies, and you then have a big tax deduction against your big W-2 income because your passive losses are no longer limited with your big material participation, it increases your audit risk a ton.

The first way is build a team large enough to do it all in house, now you have a crew lead who can go estimate time and materials to get jobs done. 

Reading/listening to bigger pockets material (books, podcasts, etc).

Many sophisticated Sellers will want to try and understand which Buyer possesses the highest probability to close and materials like this can certainly assist.  

Even Do Hard Money that advertised 100% 100% you had to spend 3k on their training materials up front and spend 600.00 per loan submission.. so you needed up front money and also have to advance on the draws..

For the course I'm looking into, they not only present some educational materials, but AFAIK also offer their resources in each market (i.e. lenders, PMs, inspectors, etc..).

It will cost about 2.5 times more on material as well as install, but something that will look nice & last you many years to come.