I have different extensions setup in 22-04 for different ring groups and different ring groups setup in 22-05 for the incoming trunks. What is the proper programming for 22-06 Normal Incoming Ring Mode and 22-02 Incoming Call Trunk Setup to make the lines ring in to the specific ring groups for each line? The calls then forward to the automated attendant after 15 seconds.

I always use virtuals, DIL a trunk to any virtual, let's say 250, assign that virtual to one of the keys on the phone, doesn't have to a physical button, example if the phone is 12 button you can assign the virtual to button 24. Program that button to ring, you can also assign different ring tones. You can setup 250 as subscriber (assign voicemail key 250 to one of the buttons on the user phones, it will flash with message) or you can assign 250 as a routing box.

I found this way to be less of a headache than ring groups.

If the virtual extension button represents inbound calls through DIL do you still have to trunk keys for for outbound calling and to place inbound calls on hold?

All the SL2100's I've installed were with analog trunks, so yes to your question.
The SV9100's with SIP or PRI trunks I use CAP keys.

Depends on how many POTS line you are using. Pushing 8 I usually suggest going to CAP/Park key route. I can't remember the last 12 button phone I installed.

I like to use Hybrid/Loop Keys for my outgoing calls. There are no Cap Keys on the 2100 And set Park Keys For Your Hold. You can still use Hold but have to Pick them back up to transfer.