Why can't I uninstall the Mountain Lion Server?

Background

My windows laptop failed and my iMAC's hard drive was recalled recently. During this time I decided to buy a MacBook Pro and migrate everthing from my Windows laptop. I also bought Airport Extreme. As I got recently unemployed, I wanted to create a private network accessible from my MacBrook and MacBook Air (until I could afford to buy the Mac Mini Server). So I downloaded the Lion Server from the App Store using my MacBook Pro (I didn't realize it would install automatically). So, I redownloaded from my iMac and went through the configuration.

Issues

• I was unable to log in using my existing user accounts from the MacBook/Air. I turned on the screen sharing (as I had lots of applications and documents on the iMac). But my firewall reported access to screen sharing service, web service etc from external IP addresses. iMac frequently went into freeze modes (no response to mouse/keyboard) and sometimes blank screen (monitor off). So I turned off screen sharing.
• I struggled with finding a way to make the local accounts into network accounts. I even tried adding them to a Network Group. I was unsucessful in being authenticated by the iMac server. The login window always showed "... unavailable ..". I went through and tried all suggestions posted in this site. Nothing seemed to work.
• I decided to unistall the Server and do a fresh install. Even here there were no clear documentation/instructions with the server app. According to suggestions here and as per this http://support.apple.com/kb/HT4827 article, I removed the turned off all services, deleted the Server.app and also the /Library/Server folder. Rebooted. The iTunes store's purchased page still shows the Server as Installed. I did the same on the MBP and it shows up asInstall.
• I don't see any of the server applications in the Activity Monitor. But my firewall reported incoming requests to Kerberos, Port 464, 5000, 625, 749, and Program Linking.
• Airport Extreme is letting in external requests. I did not use public domain for my server nor any dynamic dns service.

Questions

• How do I remove completely the Server app from my iMac?
• The first time I installed the server, I used it to control the Airport Extreme. So how do I reset the Airport Extreme to factory settings (assuming Apple's marketing literature is correct) so that it acts as a barrier between the wild, wild internet and my home network?
• Is there better control of the Airport Extreme base station? Like MAC filtering?
• How do you elevate existing users on iMac to the level of network users? I want any of my family members to be able to use the MBP or MBA using their own account and see their documents and settings.

Recommendations Solicited

• I cannot add a Mac Pro/Mac Mini Server at this point (unless Apple comes out payment plans for the consumers). That is why I purchased the MBP/MBA from BestBuy. So need the best way to use my existing resources to create a small home network for school, development, testing etc.