My contract with my property managers requires my approval for any expense over $500.

If they sell them on amazon, they likely don't require any special handling.

Just my personal opinion - get a mentor or a person who already has good experience running STR business, preferably in your area (but not 100% required). 

The seller requires a cash purchase & I’m exploring creative ways to structure the deal.

I have two options 6.625% 30 year or 6.15% 15 yearI want to invest aggressively in the near future on more propertiesThe loan is only $110k and the monthly payment for 15 year is $563 and $750I will earn 2-3k a month in gross rental revenueThe property is in a declining population areaRecently rennovated, and all major things were relatively recently improved such as plumbing, the roof, a/c, electric, etc.Will require a lot of management as it is rent by the room so I may switch to a normal rental after 10 yearsI'm trying to find what will mathematically net me the most money in the long run.

If you ask the manager to justify a fee and he starts hemming and hawing, move on or require them to remove the fee.

These types of properties require experienced management to navigate the challenges effectively.

But is there a requirement that you need to full fill before making your first post?

I may be able to STR a spare bedroom but that would be for later.Background: A fixer upper, but I do not know how much fixing is required. 

The capital required for Denver, and limited cash flow makes it a tough market to get your next one.