Need additional information.

What size is the porch, how high is the ceiling. etc.

Typically a 6" recessed, damp location listed, fixture should suffice for a 9-10 foot ceiling spaced 6' center to center with a 42W TRT lamp.

I would install 5" recessed fixtures with a black,not white baffle,and 50PAR30 bulbs.
You should always avoid placing fixtures in front of windows,unless they are tiffany style glass, and you want to appreciate them from the interior space.
Install the fixtures so as to highlight the exterior finishes and features of your home.
Uniformity of light is unnecessary , so make lights show of your home.
You only need an average of 10' spacing to obtain good lighting levels.
If you have invested in an attractive front dooe, think of installing a 4" low voltage MR16 recessed fixture , also with a black baffle

Norm, can you explain reasoning for black baffle? I want to add recessed lights to my front porch while we're redoing the ceiling, picked up 6" damp location ICAT cans that came with white baffles/trim in a 6-pack "contractor pack". Is there any reason to buy new ones?

I figured I'd space them 6-7ft apart depending on where joists are (builder was supposed to do 16" OC) on my 48-ft long porch. Means there won't be one centered on the front door, but we have coach lights to each side.

I have 12/2 "interior" Romex, same as electrician used in our fully-soffited uninsulated garage, so I figure that should be OK for the porch lights as well?

The white baffles may look good against your souffit material, but I don't believe that anyone looks at souffits.
But once the lights are turned on at night , each fixture becomes a "glare bomb" that really detracts from your home's appearance.
With the black baffle, the glare is baffled,letting the ligth highlight your home's facade.
I suggested to use one over the door, so that you will highlight your front entrance...usually a feature of your home.
I can`t count the number of times I`ve driven past homes where I can`t even see the door because of the bright lights..what a waste.
If you want wall fixtures, use 10 or 15 watt lamps, and let the recessed fixtures highlight your door.