How many rental units should/could I own? liability issues?

[RANJAY SINGH]

Need expert's opinion on few things in my head:

1. Does anyone see any issues/risks in owning more rental properties say 20+ or 30+ each with positive cash flow of $300/month approx with 15yr mortgage,  if I could afford to get loans?

2. Also how do I protect myself with potential law suits?  LLCs? S-corp?

3. Should I go with cheaper units approx 50k price range with same monthly cash flow or higher priced $150k+ rental units, same cash flow $300/month?