One Apple ID, two phones, diff amts of storage (only ONE user)

Sorry for getting shout-y, but all the 2 device/1 account questions I'm reading involve how to manage/share/hide between two users and that isn't my issue.

I have an iPhone 4. I recently got an iPhone 5. The 4 has 32g of space, the 5 only 16. I'm an app junkie. I don't use iCloud (and would prefer not to if possible), don't use photostream (at the moment). I always sync by cable, directly to my computer.

I couldn't pass up the 5 since I got it for a great price, but the lack of storage is an issue for me until I get my storage/charging case in a few months. My plan is to use the 5 as my "phone" and keep on it the apps I use most often. The 4 will have everything I use, including the memory-hoarding games and podcasts and music. Plus as I come across more apps/games I can dl them to the 4, try them out, and then if I decide to keep them, load them onto the 5. My IP/SIM is going to be transferred to the 5, the 4 will be wifi-only.

I just synced the 4 and updated/backed it up. I am currently syncing the 5 to the same Apple ID on the same computer/iTunes account. I have already gotten the warning that there is not enough room to install all the apps, which I expected. My 4 is 1 G short of being full.

These are my questions:

- will I be able to get my iMessages on both? (I assume yes to the 4, when in wifi)

- if I was to turn on photostream, is there some way to be able to have pics/videos I take easily transferred between the two phones? Since one has more storage, if I could send stuff to the 4 until I get a chance to sync/backup, then delete it from the 5 to save space, that would be cool. (Also handy if I need a pic on the other unit which isn't with me).

- what happens when I sync? Besides the two phones having different content, one has half the memory of the other. I'm worried that each time I sync it will overwrite with the other phone's content, etc.

For that last one- I have debated transferring my Apple ID to the 5, and once everything is set up properly, creating a new Apple ID for the 4, and then putting all my **** on there. That way I can sync each one without cross-contaminating each backup. But I really like the idea of being able to go into the app store and just pulling in whichever apps I already bought on whichever phone without having to log in/out.

Which is the better way to do this?