You are doing your homework well. Any of the three options will work for you: MacBook Air (MBA), non-Retina MacBook Pro (MBP) and the Retina MacBook Pro (rMBP). They all cost about the same ± $100 and they all provide about the same performance, with the rMBP faster on graphics processing (~25%). So the decision is really about features and your personal preferences.
Here is a lively link that notes PhotoShop with Retina support was released a year ago.
https://discussions.apple.com/thread/4576667?answerId=20649009022#20649009022
The MBA is a bit ligher (3 lbs. vs. 3.5 lbs.), a little less expensive ($100), and a little slower. The rMBP will be better for PhotoShop processing at only $100 higher cost.
> Also I am not sure what I can use 'Thunderbird' for, and don't feel like spending a ton on new peripherals.
Both systems support Thunderbolt and USB 3.0 connections. Peripheral compatibility is not and issue. Older USB 2.0 peripherals are compatible with the 3.0 ports and USB 3.0 disks run just as fast as on Thunderbolt.
All of the new Macs will come loaded with Mavericks.
On the MBA and rMBP you would need an external SuperDrive to watch DVDs. If you want it built in you would need the non-Retina MBP.
For any of the options select at least 8 GB of memory.
For permanent storage if you select the MBP it will come with a 500 GB or 1 TB disk (less expensive and slower) or with various sizes of SSDs. The disks are fast enough for most people and if later you find you want more speed you can always upgrade to and SSD.
If you select the MBA or rMBP the RAM and SSD storage are not upgradeable so you need to select exactly what you need at purchase time. As I noted the RAM sizing is easy: 8 GB or more. The storage size configuration needs a little more consideration. How much storage do you use on your current Mac/PC? How much more do you expect to use on the new Mac? The base configuration is 128 GB of SSD. The 8 GB RAM, 256 GB SSD rMBP costs only $100 more than the 8 GB RAM, 128 GB SSD rMBP models so it does not cost much more to have the larger storage. 512 GB of SSD is possible but that starts to get expensive.
MBP 8 GB RAM, 500 GB disk: $1,300 4.5 lbs. with internal optical drive
MBA 8 GB RAM, 128 GB SSD: $1,200 3 lbs.
rMBP 8 GB RAM, 128 GB SSD: $1,400 3.5 lbs.
MBA 8 GB RAM, 266 GB SSD: $1,400 3 lbs.
rMBP 8 GB RAM, 256 GB SSD: $1,500 3.5 lbs.
MBA 8 GB RAM, 512 GB SSD: $1,700 3 lbs.
rMBP 8 GB RAM, 512 GB SSD: $1800 3.5 lbs.
