For example to invest a million, you can buy one house with 250k down payment, 2-3 years later you can double your investment as house appreciate to 1.2MM. rents will be low, and you will loose 30-40k on interests net of rents.

The more equity they have the more I would have to loose . 

@David VaughnIn general I agree with what you have said however I have had this happen......house sitting for 6 mo, make an offer at asking, be told there is a new interested party, not adjust my offer because I think they are blowing smoke, loose the deal because there was another offer.I think it is common place for agents or wholesalers to re engage tire kickers when they get an offer.At the end of the day I tend to offer what I am willing to pay no more no less.

This would be one of the quickest ways for you to loose a lot of cash.  

. $40k seems excessive for this type of project.

For short-term rentals, the same would likely apply, assuming you offer what others don't AND you have a reliable way of screening for animals that cause excess trouble/mess OR pet owners who are not responsible.

Don’t be free and loose with your friend’s money. 

Can anyone tell me if carryover basis restarts at 27.5 years in a 1031x, or is it excess basis at 27.5 and carryover picking up where it left off?

However, I'd advise steering clear of Harris County, particularly in Houston, due to the excessively high taxes.

As long as I don't loose money I will be happy TBH.