Manually programming? You really should get Win500 or something to use as a programming aid.
Before even starting to program, you should think about what sites you will reliably here.
1. Will you use the scanner in a mobile/portable environment? Or will the scanner be used predominantly at home?
2. What MARCS sites do you think are close enough for you to receive reliably? You can determine that by programming the control channel of each site you may want to listen to via TUNE mode and see if you get a good signal on the control channel. If you do, then make a note of that site as being one of the sites you want to scan.
Once you have a list of sites, determine which talkgroups you want to monitor [and be prepared to enter them in manually]. I typically have a dozen or so I want to add in as labeled talkgroups, and then I just add a group wildcard talkgroup to cover anything else.
Mike