Below are a list of presses I have and what I like about them......
Co-ax: Preset dies make for quick painless die swap, and the lack of shell holders are the big pluses for me. I did a couple mods as well, extended tube so primers fall all the way down to a bucket on the floor, and an adjustable jaw opening shaft to shorten stroke for small cases.
RCBS Ammo master: Large Ram, Lots of leverage makes forming Brass a piece of cake, plus lots of room for your hands......Down side, Long stroke. Primer dispenser is center of ram, but exists out the side at the bottom and can get jammed up....I wish it went all the way down and out the bottom.
RCBS RC Supreme:Better spent primer containment.....But not perfect. I removed the press primers arm, and filled the slot in the ram with a split rubber tube so the primers don't fall out the front and it works well. This is just a good handy press, and will probably always have a place on my bench even if there isn't any "Favorite features".
IF I could build my own press: It would probably be a hybrid of the above.....
Primer dispense out center of shaft at bottom, a Co-Ax shell holder and die slot and a different style handle/location than the CoAx, more like the RCBS for more leverage on resizing large cases.......
I wish you luck on your endeavor! It sounds like a fun project, and even if it flops you are sure to learn a lot in the process! There are people who live in their comfort zone, and those that like to stretch theirs, Don't let someone on the internet, that you don't know, tell you you can't do something.....(Unless it's something that could kill you....You might than at least look at where they are coming from)