Do you need LEDs, or any other fancy features? Does it need to support QMK? Do you want NKRO?
Also how small is a small fee? PCB design is an involved process. What's your budget like?
NKRO: definitely.
QMK: I don't know anything about the firmware side but the best stuf on the market for custom can't hurt. At least a Corsair K70 Rapidfire equivalent, close to or better.
I made a little wishlist in this post:
https://geekhack.org/index.php?topic=91764.0Then decided hey if I'm going custom I might as well have my own layout.
Here is a copy paste of some of the main points.
This is my ticklist as minimum requirements.
-75-80% sized compact layout with F1/F2/F3/etc right above 1/2/3/etc.
-ISO layout support (so I can have an extra key between left shift and Z):
https://deskthority.net/wiki/ANSI_vs_ISO-antighosting and at least 5+ N-key-rollover
-functionality to rebind/remap any key on the keyboard e.g. turning the key between shift and Z into 'fn' or 'altgr'.
-macroable keyboard (preferably with a non-code software, like Logitec's suite)
-Cherry MX Speed switch support, this switch only has a 1.2mm 'actuation' aka travel time:
http://www.corsair.com/en-us/k70-rgb-rapidfire-mechanical-gaming-keyboard-cherry-mx-speed-rgb-na-wire connection
BONUS but not necessary
-Being able to load between at least 2 profiles on the fly. E.g. one profile can be configured to have a numpad style in the middle of the keyboard when I am working in a software with just numerical entry (this is a MAJOR bonus).
-USB stick support
-mic jack
-keycap lighting functionality (would actually be kinda cool if it doesn't add a ton to the cost).
-optional wireless support via a detachable cable
-PlugNplay