Just got a '96 prizm, few minor problems, have questions

Just got this prizm for my girlfriend, and will be tuning it up this week. It needs to be reliable.
It's a '96 with a 1.8, automatic and 150,000 miles.
So far the only concern is this strange bump at idle. It vibrates at idle in or out of gear but every so often it has a random miss or one cylinder fires extra strong. Any ideas what this might be? It idles around 650 rpm, is this the normal speed?
Runs great at all speeds while driving.
Everything looks clean, but tomorrow I am going to pull the plugs, and dist cap and replace if necessary (they could be new for all I know).
I'm also going to run some seafoam through the intake, change the filters, etc.
Also the OD light never shows up, not with the button or key on test, is this a simple bulb to replace?
And the outer drivers door handle is broken but useable, is that simple to swap out? the linkage must need adjustment too because it seems the inner handle is pulled out almost all the way before the door opens. I'll leave all that alone unless it typically gets to the point the door won't open.
Sorry for all the questions.
Heres a link to the ad http://www.autotrader.com/fyc/img_popup.jsp?car_id=232045098&photoIndex=0