DH and I embarked on the REI journey in 2011. We researched and read for a little over a year. Our financial options kept changing as we scoured the land for that elusive down payment. We looked outside the box and for our first property we found (and still have) a silent partner.
The caveat to your down payment is that you need your money to be seasoned at least 90 days. You cannot call your dad and say hey I need 25k for this awesome investment, you said I could borrow it and I am ready for it now. So, be sure to round up your $$ sources well in advance to make your underwriting process go smoothly.
So for instance. In the middle of our 3rd property purchase I sold an RV and horse trailer, We did NOT think and just tossed that money in our savings account, alas it was the account already documented on our loan as our down payment proceeds account. While in underwriting I had to go dredge up "proof" of where those funds came from, and the amounts were well over and above the amount of the down which we already had record of much longer than 90 days. Some underwriters are very, very picky.
Property #2 was financed by (don't shoot me) DH's 401k. He hates the stock market, he had no interest in managing it and at the time we were too heavy on the stocks side (I have a substantial 401k). Reluctantly I agreed. He took the 10% penalty hit. As a result we net $1200/mo from that property. Technically that 10% penalty took 8 months to pay off.
We were buying at the tail end of the crash and properties were priced very well. They went so fast it was a feeding frenzy and each property felt like a battle to end up being "chosen" as the winner of a signed PSA.
Your market will be different. You might do all this research and decide to hold on a serious property search. Our market is in a bubble right now and after buying in 3 consecutive years, we decided to hold off this year.
Property #3 was not as sweet a deal as the first two, and it is an odd configuration with a shop that took forever to rent. We used a heloc to fund this property. With that shop rented it cash flows as well as #1 (not quite as well as #2) so it does have a weakness I would rather not have to deal with.
Ok, so I've covered financing. Now as far as mentors go. I highly recommend you get to know a great realtor, a trusted clever mortgage broker who can make your financing as painless as possible and fellow investors to run ideas by. I was fortunate in that I already had real estate investors in the family, a close friend and unbeknownst to me, my cubie neighbor at work. I found him to be the most helpful because he owns multiple properties, all sizes and has had them for a decade (he won't tell me how many, but he has spoken specifically about five, I just need to keep digging for more stories I guess). I still like to swap stories with him. I never did go to a local investor's group. I still read all the case studies and war stories on the Bigger Pockets forum, this forum and any other forum I can find.
The best of luck to you!