Looking at the steps you have listed, I'm not sure you'll accomplish what you want.
1) for a 'centralized' dialplan, most customers will use SME. Because many of these customers have UCM already, SME makes sense since it's UCM w/o any endpoints, just aggregated dialplan and SIP trunks. CUBE can be used, but CUBE typically serves as an SBC between the customer network and various service providers.
2) If you replace the SCC/MCC with a 3945, what is doing call control for the phones at the site. If SCC/MCC is removed, will the phones register as SIP UA's to the 3945?? I would expect you to connect the SCC/MCC to the 3945 to provide connectivity to the SME (step 1) for centralization of the dialplan and PSTN access.
3) add a UCM cluster....that's needed to replace the Avaya :-)
4) not sure why make a SIP trunk here....should have been done as part of step 2. Setting up 3945 as SRST is good for when you replace the avaya handsets with Cisco Phones.
5) After the endpoint replacement (and tested of course), the migration is done. The last 2 steps are housekeeping.
Since the steps described in your post are pretty general and not specific, I may have misread what you are planning on doing. If so, please repost clarification and I will answer as best as I can.
Technical Marketing Engineer