If you are still making payment on your present home you may be required to lease it out in order to qualify for the loan amoumt you want on your next home. If you are lucky enough to contact an agency that can guarantee you a lease for a certain amount it will be a plus mortgage wise.
Happy House Shopping
I have many clients that have done what you are doing, and they are on to their fifth and sixth home, ensuring themselves a healthy retirement income and more financial stability than your average person. My typical client rents a home for about 1% per month of what it would sell for (though that is fairly aggressive in todays market) and then gets the increase in equity.
Since your primary residence will become rental, you should check your mortgage agreement with a lender. Probably there is stated that if your primary residence becomes rental you will be in breach of contract and they might call the loan due. I do not think that this will happen with all going foreclosures, because they have better things to do right now then to check what primary residence just became investment property.
Depending on your equity situation in your current home, and how much you intend to put down on your second home, you may or may not run into lending issues. Some concerns are:
Will you have your existing home rented before you purchase your second home. If not, then you'll likely have to qualify for the second home under the assumption that you have no income from your existing home and the full payment will be factored into your total payment ratios.
If you have a lease signed for your existing home, the lenders will typically only consider a portion of the lease payment as offsetting to your current monthly payment for it. I've seen numbers from 50 to 75% of the lease payment applied towards your monthly payment in determining your debt ratios.
There's no real negative to be concerned about from anyone's perspective but your own. That is, how comfortable are you that you can rent out your home to a consistent and long term tenant? How comfortable are you should you have an interruption in rental income? Do you have the resources to manage the existing home once it becomes a rental.
Try to find an agent who has experience dealing with rentals, when you search for someone to help you buy your second home. They should be able to provide good advice on the ins and outs.