Not too sure what you mean by "Tier 2". I would assume you mean "middle of the pack" iMac - within the 21.5 grouping (as shown on Apple Store).
What to focus on?
- Is the screen size right for you? Some think the 21.5" screen size is perfect. Some like the 27" much better. And, some (like me), feel the 24" (no longer made) would be a perfect size. Hopefully, future iMacs will come in 24ish sizing. Perhaps future iMacs will be in the 24-25" range? Only time will tell...
- What HDD size to pick. Some want 500GB, some want 1TB and some want 2TB. If you install small size now and NOT a DIY person, installing a much larger size HDD in 1-2 years is a PITA. And, can be expensive - if you get others to install it. Thus, it might be worth getting a much larger size "now". Once you have a larger size, you have it (when needed). A wise man once told me... Determine size of HDD you need now, then double it. Then, round up to the nearst next available HDD size. That's how much HDD space you'll need in the future. Next time around, I'd get the 2TB drive within my iMac.
- How much memory? Its always based on one's specific usage. Majority would agree to buy "more" memory via 3rd party. Apple memory is expensive - compared to others.
- Track Pad, wireless Magic mouse or 3rd party wired mouse? These are personal choices.
- Normal basic keyboard or larger keyboard with numeric pad. This is a personal choice as well. I do know that many fiancial folks love their numeric keypad area. We love our larger sized keyboard as well.
- Programs. Buy bundled or afterwards? Your call on this one as well. My wife loves Pages better then MS Office / Word. Only install MS Office (which is very expensive) if you are a MS Office junkie.
- Get their suggested printer or use you own (existing) printer? For my family, we bought a new iMac with bundled "needed" apps. I then took my existing PC Printer (usb based) and plugged it into my iMac. As expected, it recognized my printer, installed needed drivers (later, it even auto updated newer version drivers) and it worked great. Because our existing printer (with included Scanner feature) worked on our new iMac, it saved us the cost of a new printer. If you have an existing printer, tell us its exact name / model. Folks will tell us if they use the same printer on their iMac system. Thus, saving you from buying a new printer with your new iMac as well.
- I'd recommend buying an external drive (for automatic Time Machine backups) as well. Can use a self powered USB portable drive or a larger size "vented" stationary external drive. Personal choice. But... I do recommend getting a larger external HDD with your new iMac. Especially if your data is pricess (like family pictures and stuff).
When buying your future iMac, do keep these things in mind...
Good luck...