Having multiple properties, great idea or no?

I've currently had my home under a fha loan for the last 6 years. I'm in the early stages of a refinance to switch to a conventional loan so that I buy FHA again. I'm 32 living in the Bay Area and think that would be a good idea to have multiple properties, one rented out and one as my residence. Would be beneficial for me in the long run? Or am I in over head?
P.S I can afford it, if the rental has a paying tenant in it.

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