What is the STR registration process with the City (I couldn't find any info)? 

If you want to rehab in that market, perhaps spend some time networking there and maybe you will find someone whom you can partner up with who has experience in the local market and with rehabs.

I tried to google but could only find vacantion-like sites with exorbitant prices.- Is there a kind of person who could help me with pre-sale improvements (roughly saying, to tell me what is worth replacing, improving, etc and what is not,1 to make the house more attractive for the buyer)?

How do you know this property will even cash flow at the $390K asking?

WEst coast  OR WA AZ NV CA etc is all cash on the barrel head there are no deposits and no over bids.. winning bidder presents the cashiers check and they have won the deal on the spot.

I can't even count how many times I have seen posts on Biggerpockets from struggling investors trying to rent out Section 8 properties or D class properties out of state.Everyday there is a new post from a Newbie Investor who put their hard earned cash into a dud of an investment and cannot figure out why they can't find a solid tenant, why their tenants don't pay, or some other horror story related to investing out of state/D class real estate. 

I want to buy him out because the property has a 3% mortgage rate, has gained 100k in equity the last 4 years and cash flows 1k a month.

Quote from @Mei Zhu: If you signed a contract, you are obligated to honor it even if you found the house on your own.Real estate agents do a lot more than find houses.

@johnmason, I have completed a BRRRR over Covid but that was in a different market since then I moved into a more expensive market due to my full time job so finding a deal has been a bit more difficulty

You cannot find any other reviewed and vetted companies in this forum?