I would start with cash and then move quickly into borrowing.
The reason I would start with cash is because based on your post, you're limiting factor isn't going to be capital starting out, it's going to be building a team that can renovate, manage, rent, find deals, etc. However, once you have line of sight to having those things in place and can start to build your business I would quickly look for financing. Don't underestimate the time and potential hurdles you could face getting financing. The opportunity cost of waiting is too large! Borrow sooner, rather than later.
Please take your personal preference into consideration. Mathematically it's almost always better to borrow if you can invest at a higher rate than you borrow at. So if you can borrow at 5% but get 10% returns, the more you can borrow at 5% the higher your ROE is and the more money you make. Think about it, that's how banks make money! However, you're not a bank or a corporation so if you are uncomfortable handling and managing debt take that into consideration.