These two seem like the most obvious ways to get motivated sellers to contact the buyer first versus the investor buyer having to hunt for motivated sellers.

For example, if I have a primary/second home mortgage on a property that I turn to a rental property years down the line would there be any differences in tax benefits I can take advantage of versus a property I buy using a investment mortgage?

We have a storage facility that took forever to close because of SBA shutdown and our rate we are getting versus quoted was .92% lower.  

2) if you buy and house hack how much more can you save per month versus current rent situation?

If you do Option A you will have to pay capital gains tax on that $500k check, that could be very costly, versus Option C which is not a taxable event.

The same would apply to attorney fees, to some extend reno costs - single large roof versus 5 individual roofs and etc.

You can always go do it on your own for the first deal but if working with another investor in a partnership is the starting point versus not starting at all, well thats a easy call in my opinion.Note, I highly recommend consulting an attorney and writing up a JV agreement for the duration if not a creating a LLC to which you would transfer the deed after purchase.

If your goal here is to get familiar with the underwriting process then you should get the same value from underwriting a good deal versus a bad deal.  

The caveat is this: He is going to rent for two years below market value, which is fine with me as I will still cash flow about 200/mth versus 600. once rent is raised. 

There very well be other options than doing a full 75% etc cash out refinance, but still utilizing a cash out method versus HELOC.