Work on getting your CPA designation with a Real Estate Focus.

Personally, I'd factor in the cost to put each unit on it's own electric and water meter in my offer to purchase.

In general I have Realtor contracts, they are designed to protect the realtor and do not represent the offer I want to make.

One factor left out so far is income tax deduction implications due to the unit that is below market rent ...

Lots of factors to consider, many already mentioned by others.

On conventional loans for investment properties I know they try to stick to around 45%, but will go up to 50% with high compensating factors (credit score 720+, high cash reserves).

But unfortunately that is theoretical, and you also have to factor in transaction costs of selling and buying something else, tax implications (1031?)

But if it will cost a lot, be sure to factor that in to how much you want to charge for a month to month.

If you borrow from your 401k, a lender will want to make sure your current income(without the rent from the property you're buying) will be able to handle the new Principal, Interest, Tax and Insurance payments on the new place on top of the 401k loan monthly payment.When you run your numbers on a potential property, factor that 401k loan into your debt expenses so you're not running in the negative every month (defeating the cash flow purpose).

Depends on how much cash you need.These are all pretty straight up deals, we can get wilder or more creative, depending on many factors of the multi you find.