How much should I look to save for down payment?

. - I agree with you that purchasing rentals now is another great solution which we are also doing (mainly in the name of supplementing retirement though).  

So far on both properties, we have just used our savings.  

I'm interested in the idea of working in a real-estate related job while saving toward buying more investment properties.

Appreciation will not save you over the long haul, look at the situation in the present.

@Jose Jose, glad to hear you're thinking about this- water savings are an amazing way to increase your return.

***What I would like to do***I would like to be able to retire in the next 15 or so years on a mountain of rentals.  

Many landlords sell with owner financing when they want to retire from rentals.

The single loan aspect saves a lot of money due to the fact that you only close on one loan.  

if he takes care of all that it may be worth it, figure out what your costs would be to hire outside services and see if it saves you money, is the place that big that you need an onsite manager or will it cost you less to hire a PM company ?