Cheeze, hey bro! I would try the following in order to see which one will remove the glue: Goo Gone; acetone (carefully - test an area and don't dwell); wet sand (600 paper) followed by heavy-duty rubbing compound. I had some residual glue from the prior owner's removal and ended up doing the last approach since I wet-sanded and compounded (machine) the whole coach and brought it back to a nice shine. It actually wet sanded very quickly smoothed out a lot of "grain" that made the gel-coat look dull.
As for the table flange, Cabelas has some nice seat flanges and posts that could be used. I used their flanges on a restored boat for mounting the captain's chairs and they are pretty flush with no big hole in the middle. There are several types to choose from.