Tim, if you can get 100% financing that's great - it gives you more money to invest elsewhere. Of course, it makes your loan higher which means higher monthly payments so be sure you can make those monthly payments.
Leverage is great, but it cuts both ways - it can magnify your return in good times, but it can also magnify your losses in tough times because you have a fixed payment that needs to be made every month whether the unit is rented or not, whether the rents are high or cover the expenses, or not.
I would caution you to ask yourself, if your other unit was vacant for 6 months, could you carry the loan payment on your own without difficulty?
If yes, then you're probably in a good position to take on that loan. If not, then you may want to re-evaluate whether it would be better to put a downpayment down (if you have it) to lower the monthly payment, or maybe look for a cheaper property (and thus, a lower loan amount).
(6 months vacancy may seem too conservative but believe me, I've seen 3 months before without extraordinary circumstances - tough rental market, area declines, you missed something that makes the unit a harder sell to tenants, departing tenant caused major damage that takes a lot of time to fix and then bring it back to rentable condition, you do things on your own so you save $ but it takes longer, etc.)
It sounds like you're comfortable with a 2 family and if you're just getting started that can be a good way to go. Just be careful that, as I said, you can afford the monthly payment on your own - the rent from the extra unit should be "gravy" (bonus), not needed-or-you're-in-trouble.
Also, while singles and duplexes are good for lower maintenance (tenants have a little more "owner" mindset), you'll also pay more per unit that way, mainly because you're competing with owner-occupants who are buying primarily for the "use benefit" (they like the house, the neighborhood, schools, etc.) and not looking at it as an investor. It sounds like a worthy trade-off for you, to do a duplex, especially if you're going to live in one of the units, but it's just something to be aware of.
I'm not sure what you mean about "profitability of the long term investment over time". If you mean, planning/projecting for a big profit down the road, I would forget about that. You're buying at a good point in the market cycle, if you sell down the road and make more profit, that's more "gravy" (nice to have), but don't count on it. Focus on whether the property will cash flow in the first couple of years and whether you can support the property if you have an extended vacancy.
If you haven't already seen it, check out http://www.biggerpockets.com/rei/real-estate-property-analysis/? for analyzing whether a rental property will cash flow (i.e., produce enough profit after expenses).