Good questions....but no easy answers.
1. Nothing quick about checking liabilities....this is time consuming. You have to do a title search and other searches like bankruptcy. You have to either pay for title searches or learn to do them yourself and feel comfortable you really know how to do it with the resources you have. Chances are there are no mortgages that will actually go to sale and get sold. If it is a nice house with a mortgage, chances are the owner escrows, or if not the lender will pay Monday before or morning of the sale, and property will get pulled. Pretty much all governmental liens will stay with the property like mowing, demo, code violations.
2. You have to determine what your risk tolerance is. Everyone is different. Everyone has different skills and headache tolerance. Just to give you an example...I don't like old single wide mobile homes. I can't ever imagine I would buy one even if it is $100. There are plenty of people who buy these. I've seen $50 lots for sale. I don't want to mow or have those mowed for the next 5 years and owner finance $1000 lots in small towns that have not had any homes built in 20 years and probably don't have utilities to them or if they do it is 80-100 year old water and sewer lines that you'll mess up when you try to connect. Those are just headaches I don't want to have at this point in my life. There are people who do like these headaches.
3. For the most part you won't be able to sell any of these properties for 2 years. Just keep that timeframe in line. Forget the six month idea. Chances are no title insurance for 2 years, so with no title insurance, no one will probably lend on them. Certainly no normal bank mortgage financing. Why would I buy with a profit to you if there is a chance any spread I pay you could/would get wiped out if owner redeems or challenges the sale. Sure if you buy for $50 and sell to me for $100, maybe I take that chance and you double your money, but when and where does that risk stop. I'm not probably going to buy for $200,000 if you bought for $100,000 and risk loosing $100K if owner redeems....no matter what ARV is. Are there exceptions, sure...but they're more the exceptions than normal reality. Almost nothing that sells is occupied, so don't really plan on that. If it is occupied, rare is it the owner. Can you lease, sure, but in reality most and I mean like 99% are not move in ready. You probably won't get reimbursed for the improvements you will need to make to get them ready to lease, so if you improve them enough to get them leased you add risk. If you do lease them, you probably want to do it on a month to month basis with the full understanding that the property could get redeemed next month and tenant then has to move out...could be 2-3 months, could be 24 months, just never know. I would expect you would not get full area rent for most property. Maybe you have to rent 1/2 price or 1/3 price of area comps to encourage someone to take on that risk of short move out. My normal advice is plan on holding them without income for 2 years. Plus you will have taxes, insurance and potentially some maintenance for that two years.
4. Harris County is probably the most competitive in the state, perhaps with Dallas, Bexar, Fort Bend, and Bell. Not sure there are stats or real data to back that up, but you might see 300-500 people at Harris, 300 people at Dallas. Of course there are a ton of properties on the list in Harris...so more properties, more population, more bidders. Smaller counties typically have fewer bidders. I have a nice story about one deal I bought where the sale started with 2 people, me and one other guy. When he learned about minimum bids he had to bail as he thought bids started at $1. So I was the only one left. That's pretty rare. Depends on what you want to buy, but I would say most sales are competitive. There are deals, but you really have to do a fair amount of work to find them.
5.Drive every property you plan to buy. NO exceptions to this. Google is your friend to eliminate properties, NOT to decide what properties to buy. Skip this and someday you will get burned. KNOW 100% what you are buying and your exit strategy.
6. It's a cash business typically. So plan on your cash being tied up for 2 years or longer. That solves Tax Sales for most people.
7. Just like any other niche there is money to be made, but it is work. It's not quick and easy 99% of the time. You research, you drive, you estimate, you go to the sale all day on a Tuesday and sometimes you win and sometimes you don't. If you don't win, you may do this 2-3-4 months in a row and never get one property. At that point most people hate their life, and go home and try MLM. If you win, then you tie up your cash for 2-3 years or longer. Plenty of headaches along the way in many cases. I would guess just like any other real estate niche 90% or more give up after 4 months or one deal.
Get your list, decide what you want to buy, do your research, go drive the properties, go to the next auction with your list and max bids. Don't bid, just watch. See what others bid compared to your max bid. Would you have won, lost, or not even been in the game? Then you have a better idea.
None of this is to discourage you, just to give you an idea of what's in store.