Personal credit and assets will also be used and the amount of assets you need would depend on how many properties you currently have financed.

I also know this is dependent to the states as well, but generally speaking I'm curious on a federal level. 

Time would be the biggest variable.Assuming the same repeatable services will have to be provided for STR & MTR, that are not provided for LTR, the costs may not be that different.Taking care of lawns, monitoring & paying utilities, taking calls, etc.Some services will be the same, but vary in frequency: cleanings, resupplying amenities, responding to inquiries, bookings, granting access, etc.

if they stopped paying you would foreclose (depending on state laws.)i have bought on seller finance, and i think it's a great option for sellers / investors looking to end / exit their careers. 

It really depends on a lot of factors, how knowledgeable you are about your local market, and whether you would be passively investing or actively investing remotely. 

Depending on your skill set and time would you be able to go and knock out what is needed in a couple weeks?

On average, real estate appreciates at a rate of around 3-4% per year, although this can vary greatly depending on location and other factors.

If you provide a scope of what you are demo-ing, you may have better luck with someone's experience to comment here, but costs can vary regionally, so a local contractor would give you the best actual estimate. 

I've also used GC's to complete full rehab jobs & depending on how much work a house needs and how comfortable I am with the rehab, often times I will sub out the work to different painters, handymen, electricians, plumbers, etc instead of using a GC.The more I do this the more comfortable I am managing the jobs myself and it often times saves me significant amounts of money on the rehab costs to just sub out the work vs using a GC for the full rehab.

It can depend on factors, sounds like in the ballpark but definitely smart to shop around.