I know this isn't going to be helpful, but to me it seems easier to just go with regular old Scart cables + GSCART meme. There are other options too for SCART switchers, but none are as versatile or good as the GSCART.
With that setup you get 8 inputs, 2 outputs and the ability to add a matrix switcher for more outputs should you want it. Heck you could have one of the outputs go to your extron crosspoint should you want to setup 8-16 different displays instead of buying a different matrix switcher.
Here is a good video on your options
https://www.youtube.com/watch?v=998tBzpJhVo
going the scart route also has the added benefit of using standardized scart cables instead of bnc should your extron puke. I am assuming you have to make those stupid phoenix connectors for audio too. You really need to make your own cables for an extron it to be worth it. With the consoles you listed that is like 49 cable connectors, even if you are a master cable manager it is still going to look like a giant fire daisy chained death trap like below.
giant daisy chained.jpg
For the price of those BNC cables you would be better off buying HD Retrovision cables, even though they don't have a cable for each system yet.
Here is a good guide from retrorgb on the extrons. A very good site if you want to see what each console needs in their scart cables and what your options are. Also good edumacation on RGB in general.
http://retrorgb.com/switches.html
So iirc Extron need CSYNC and the output is TTL. Most consumer devices use 75 ohm as a standard and will need to be attenuated (unless you're using a professional monitor that requirs TTL).
Most consoles output Csync, but for the ones that don't most people grab Luma or Composite Video and use a sync stripper should they need CSYNC. PS1/PS2 is a good example of a system not having CSYNC natively, but can be modded to restore it. Or you can be lazy and just use a sync stripper. Keep in mind if you do use a sync stripper It will output TTL CYSYNC unless attenuated, but also has the downside of delaying the sync resulting in a shift of 5 pixels to the left iirc. What is cool about the Gscart lite is that it has a built in sync stripper that can be flicked on or not.
You won't need a 1 chip SNES/modded mini to use it on a Extron, 2 chip outputs CSYNC as well. The only exception is a SNES 1chip-03 and SNES mini, both which can be modded/have csync restored for rgb goodness.
for sega saturn scart cables. Models 2's sometimes need sometimes need a 470 ohm resistor and 220uF cap if using csync since sega didn't put them inside the console on some revisions.
http://retrorgb.com/saturn.html
Like DeceptionZero stated, you really need to do your research before you dive in head first. I hope this helps you, if you have any other questions lmk just giving my 2cents on it.
/wall of text over