Brandon W. -- My biggest initial concern would be the distance. My units are 45 minutes away and I'm over there every other weekend. My tenants drop their rent in a dropbox and always pay via cash or money order. I'm not sure if I could ever get them to reliably mail me the rent, but I haven't tried yet so that's my fault. You may be driving over there a fair amount, at least in the beginning.
If you can cash flow with a management company than that would be the easiest. Bring them on and, if they're any good, they should bring the rents up and clean the place up. Since you're looking at a 4-unit than you're still residential and not commercial. I may be wrong, but I don't think cash flow plays as big of a part in determining the selling prices as it does with 5+ unit commercial complexes where property valuation is usually determined by cash flow. I don't know so I could be completely wrong. That being said, when it comes time to sell you could unload the management company to try and show as much cash flow as you can to try and increase your selling price.
I don't think you'll be able to get more deposit from existing tenants. There's no incentive for them to give you more money and, honestly, they probably don't have it anyway.
Long story short, a 4-unit building is a good starting point. Make sure you're honest with yourself about the cash flow. There are a lot of costs that you may not think about (extermination fees, trash, water, gas, electric, insurance, etc.) What's you're cap rate on the property off of actual values, not pro-forma (what they claim is market)? While the building may not appraise off of performance, you'll certainly notice if your cap rate is only 2% or less! I've know a few companies who advertise an 8.5% cap rate off of market value, but actual figures show a cap rate of 4%. There's nothing worse than getting into a property and breaking even or worse. I know the tax breaks may make it up to you in the end, but it's nice to have some positive cash flow every month.
Typical property management fee is 10% of gross rent. If they're advertising less, ask why....