The best upgrade I could suggest is a 1050. The swage station is really worth it when it comes to priming, even more so with automation. If you could ensure all of your brass has pockets ready to accept primers then a 650 with the most reliable primer feed out of all progressives would be a good upgrade.
As far as bullet feeders go, see if you can find one of the GSI feeders, they are the best I have for Dillon machines but I do have Hornady, KISS (before the two guys split up and the name changed to MBF) and the current MBF, they all can work.
With all presses, I highly suggest you set it up and use it as the manufacture intended it to be used first. If you decide to not do that, you will have no idea if the changes you make, make the press better or worse.
This will be even more important on you 750 with an auto drive, you should have, at a bare minimum, hundreds of issue free loaded rounds with it before automating it. If you don't you are going to get frustrated and any call you make to Dillon will not gain you much sympathy.