MacBook 5,1 Upgrade, Leapfrog to Yosemite and MBA Backup My 2014 MacBook Air was recently stolen, but I have a full backup available via Time Machine saved to an Airport Extreme base station. For now I'm using an old MacBook 5,1 with an Intel Core 2 Duo processor and 2 GB RAM.  After using the Air for so long I kind of like the feel of this machine better and don't mind of the bit of extra weight. I am inspired by all the info available about upgrading this model, and I think it's a better solution for me than buying a new MacBook.  There seems to be plenty of info available about the process, but before I dive in I'd like some input from the folks that know a helluva a lot more than I do about this kind of thing: 

My plan is to upgrade the 2012 MB with an internal SSD drive and enhance the memory, but once that is done, can I then use the Time Machine backup from my 2014 MBA to populate this computer, or will the format switch from MBA to this MB wreak havoc?  If it is a problem, can I just upgrade and do a clean Yosemite install and then just move over key files and applications from time machine to the 2012 MB?  As mentioned, the backup is saved on a Airport Extreme base station, and I have a memory stick startup disk from a clean re-install that I did on my MBA about a month ago.  Obviously I can't recreate that without my 2014 MBA, so can I use that or will it also cause issues? In the AppStore I still have the option to download Yosemite, so if I can't use that start up disk what are my options?  I'm only as good as the last YouTube video I watched about this stuff, which is dangerous.
No, your Time Machine backup should restore to a supported Mac just fine.  I do it all the time to save time installing multiple machines from scratch.