have iphone 4 and original iphone - apps updating and no longer working

As I update apps in itunes or on iphone 4, they sync back to itunes and then back to the original iphone when I plug it in as expected. The problem is as apps get updated for ios 4/iphone 4, they are now starting to no longer be compatible with the original iphone. I understand that new apps and new features won't work on this phone, but the problem is that the older version of apps that DO work on the original iphone are being overwritten by the newer versions and then no longer working (not able to be synced back to iphone 1). I have turned on restrictions on the original iphone to keep this from happening (stops all apps from syncing) until I can find out how to keep the apps on the original iphone at their current version, updating those that are still cross compatible, while also having newer versions on the iphone 4. The app store app shows 39 updates are available on the original iphone, but I am scared to allow them to update and then stop working. I use the original as touch for apps and remote, etc...

Also, is there any way to get "back" versions of apps I have purchased so I can have them back on the original iphone which is where I purchased most of them.