@Leandro Bidal What is a "big portfolio"? You can typically get 10 properties in good, long-term, "normal" loans. You can get commercial loans on them individually as well, but terms are much less attractive and insurance is more expensive for less coverage. What some people do is buy 10 "normal" home loans (Fannie/Freddie). That maxes out their personal mortgages, then have a lender come in with a portfolio loan and refinance the package. Then you have 10 more you can buy with good financing, roll them into the portfolio, etc. There are more ways, but that is just a general method you can choose to use.
I don't want to start an LLC flame war, but I would probably do entities as you mentioned. If you have access to a series LLC it might be worth looking into. Some people (typically ones that get paid based on your # of entities) will say to put every home in a new LLC. Some would say use an LLC to hold a max of $1m in homes, then a new one. I say have a good umbrella policy, figure out your risk tolerance, understand the cost and hassle-factor of maintaining multiple LLCs (different accounts, different books, different tax filings, etc.) and go from there.