first off, this an awesome wave of figures, the luke just blows my mind away, I'll definitely be buying several of those, assuming I can find them...
Well, this probably is the right place to ask, but since we are on the subject of R2 drinks on his drink tray, I have a customizing question. I am VERY new to customizing. I just tried a "simple" head swap for a custom to compete in the artoosnews.com's SH4 constest (won 8th place). I had to trim & trim the knob under the neck to get the head back in the hole. I didn't have that big of an issue pulling it out, but I could not get it back in.
Well headswaps can be tricky when talking about putting a head whose neck peg is larger than the hole you're trying to insert it in. Sounds like the case here and your solution was the right way to go. I don't know whether or not you used the time honored "boil and pop" method for removing the head, but you can actually use it again to put the head back on.
Anyway, with painting, which I have never attempted and would be nervous on something with such small detail. I think I would like to keep the current "cups" on since I think it would be a night mare to try to keep them balanced on the tray. I don't know if a small drill bit could hallow out the top of a cup, but I'd like to try that. But then what paint... grey/white? to paint the top of the cup with the appropriate drink color at the bottom of the cup. Anyone ever customize something with this small of detail? Would it be worth it?
I didn't notice if the cups were removable or not, but a simple dab of glue would obviously keep them on permanently. A very small drill bit probably would do the trick in hollowing out the cup. About painting in small details, it just takes time and practice, especially when it comes to R2 units, they're a tricky lot.

Might I suggest checking out the always fabulous
FFURG for all your customizing question needs.

Of course also hit the customizing section here at JD where you can pick the brain of many of us customizers.