I've read that this introduces risk when using a TPA, but I'm not sure whether there is material risk in practice or this is just something that someone wrote on a blog.

Here is a blog I wrote on this subject:We love our family and friends, but beware of them becoming your tenants.

Try these companies: https://www.biggerpockets.com/blogs/2810/50272-lis...

From there, check out the BP blogs and participate in the forums.And find a few local REI to network. 

I have written about my investments on my BP blog in a series of articles Have I Found the Holy Grail of Passive Real Estate Investing?

https://www.biggerpockets.com/blogs/5937/61324-can-you-cash-flow-more-renting-out-a-car-than-renting-out-a-house

I would contact each lender to discuss your particular financing needs. https://www.biggerpockets.com/blogs/2810/50272-list-of-non-recourse-lenders-for-self-directged-ira-and-401k

Lindy Peterson whether your STRs are in Grand Lake, CO, or Houston you can find knowledgeable Real Estate CPAs that understand tax treatment of STRs here in BPs Tax Professional Directory: https://www.biggerpockets.com/blog/tax-partners

If you want a day to day on my adventures check out my website for my daily blog on building with modular.I've already gone into it in some other forums but there are no real negatives in modular construction.

(POST EDITED TO REMOVE YOUR SITE BY ADMIN - YOU ARE NOT ALLOWED TO POST YOUR WEBSITE / BLOG ANYWHERE)Assuming you already have some homes in mind I would suggest partnering with somebody on your first deal so you can have enough for a down payment and at least a good $5k set aside in reserves for any capital expenses or vacancy loss for the first year.