Yes, you can install packages. kmods might not install cleanly as the daily snapshot kernel is rebuilt every day and they will have incompatible signatures. Unfortunately on this unit there is very little memory left (with the default partition scheme), and upgrading packages fills up the overlay partition, so I'd avoid upgrading things if you can.
Once you are running the tplink_tl-wpa8630p-v2-int build from my repo, you can actually sysupgrade to the official tplink_tl-wpa8630p-v2-int builds as they are practically identical, then you will be fully running the unmodified official software. The extra SupportList patch is just needed to get past the initial TP-Link firmware upgrade.
However I'd stick with that tested image from my github repo until the next stable OpenWRT release, unless you really need to upgrade. I've been meaning to test and refresh it, but my test unit is in another country until I can get another here. One issue we found with the daily dev snapshot images is that on rare occasions they can break booting (e.g. 1/50 days?). Its a problem for this unit in particular as there is no known way of recovering it without opening it up and using a flash programmer or serial cable. Happened to a few people on the forums, so we put a few warnings in the wiki (along with the existing warnings:).
Once it enters the stable release, using the default images or ImageBuilder should be safe(r) 
Yeah seems straightforward. I wrote a shell script before Christmas that uses available firmware to make a "universal" image to fully convert the flash into the AU partition layout. But when I tried it, it bricked my unit so I still need to test it more 
. I'll upload it to github at some point.