Undervalued 6 unit complex in pretty good area with under-market rents.

I am about to make my first offer on an apartment complex and do now want to screw up.

The building is in a complex of like buildings .

Great question, I had the same one earlier on in my investing journey.It is a complex question only because it depends on how the numbers work out in each scenario and which loan types you were considering for each purchase.To answer your question about the positive cash flow, banks do indeed consider rental income from the properties you have and/or are buying. 

Kind of like buying a land condo vs buying the entire apartment complex vs buying a single family w/out HOA.The other thing is I'd check to see if the Marina allows live-aboards vs. just a place to park vacant boats ... depending on what strategy you are trying to pull with the rental of the slip.

I rent a similar 3/1 unit for $1200 a couple of blocks away, but there is a townhouse rental complex nearby this unit that rents for 1100 for similar 3/1 units that appears to have brought down the rent either via proximity to that complex. 

When you overcomplicate things it makes it a lot easier to miss a detail that could potentially open an entity up to being set aside.While I understand the "multiple layer" argument, the extra complexity (not to mention extra cost, if you care about that sort of thing) means extra risk of doing something incorrectly (missing an annual meeting, writing a check from the wrong account, etc.), and if you maintain the main entities correctly anyway I think that (and a good insurance policy) is the real line of defense."

Im looking at 2 options right now, one is a complex of 4 and the other a complex of 5 (putting it into the commercial category).

IF the 15 unit complex is truly a deal then I would connect with others in your area who are interested in this type of project.  

For instance FHA will not lend on non-warrantable complexes.