-What are the pros & cons of these options- senior housing vs Airbnbs vs student housing?

So no right or wrong just different options and that takes work so if you want professional help I'd recommend you contact advisors on the forum or go to the BUILD YOUR TEAM tab and do a search for professional financial advice.   

You have options!

I think you have 3 options - Update it to HUD standards, wait for a cash buyer, or use a company like I just found with a search https://www.nhmcinc.com/now-financing-pre-1976-manufactured-...

I need to know the percentages of the options I have available to choose in order to be able to calculate the EV and choose the best option, the one that will give me the best return.

DSCR loan options will qualify you based on the market rent for the property - this can be helpful if you can support projected rent above the mortgage payment.

I've read articles about hard money lenders want to know is this a viable option? 

If you're okay with low end / sec8, you've got a lot of options in the rust belt and down south.

So it stops right there.Secondly you see folks bluster about specific performance on this site all the time and unless there is hundreds of thousands of equity someone is trying to get it rarely is a viable option. 

Another option is to take out a bridge loan for the rehab, then refi and take out a smaller amount of the $750,000.