@Yia Her I'm newer to the tax lien space. I've only participated in about a dozen sales in the last two years. But I've done well and think I have a winning strategy in my area. Time will tell. Depending on age and money, I think tax lien strategies are drastically different. I'll answer your questions.
1) Mostly Indiana deeds. Everyone says 95-97% of liens redeem but that number is much lower in Indiana. Don't know what the overall number is but mine is 23.5%. You make the money from the property not the redemption. Although 10-15% is good for a lot of people.
Although people say Florida liens are great I think they suck. After the long redemption period is over you have to bid for the deed. You either get the house for retail or your bid down %. Buying the deed is speculation and not investing.
Iowa tax lien sales are fun.
2). Don't bid too high. I think you need to buy liens in volume so I've looked at all the properties on the list. So there'll be another one.
3). All of them. While I'm looking at all the properties online exit strategies is the most important item on the list. Wholesale, rehab, rent, burn down and collect insurance (kidding but can't say I haven't thought of it). My favorite is owner financing. Collect a nice down payment to cover your investment then collect a nice interest on your profits every month.
4) Don't look at them as problems but issues to take care of. I wish the plumbing wasn't stolen. I wish there were no code enforcement liens. I wish roofs weren't leaking. I wish there was a clean title. I wish the government employees were nicer. I wish that dead body wasn't there. You deal with them
5) "Profit by investing in tax liens" by Larry Loftis
"Zero Risk Real Estate" by Chip Cummings
The books give you a basic understanding but after you understand the basics the most important thing to read is the specific county laws and rules concerning their tax sale.
Happy Investing!