The one thing you didn’t talk about is whether you expect to use a lot of Gadgeteer modules or not - that’s why Spider/Raptor have the benefit, it’s super-simple to connect them. Don’t get me wrong, I have a Cobra2 WiFi sitting on the bench in front of me, it’s great, but it’s still not the be-all-of-Gadgeteer, which you mentioned is what you wanted to try out.
P0.0/CAN1_RD, P0.12/AD6 means the following:
This is a pin known as P0.0 on the processor. It has a secondary function of the Controller Area Network port 1 (CAN1) Receive Data (RD). The second pin is P0.12, secondary function is Analog-to-Digital channel 6.
While you won’t get the full 35 extra IOs from the edge connector, you will get a lot; but again, you’ll have those plus the ones on the Gadgeteer sockets you can reuse if you want. It has more than enough IOs for most purposes, but obviously less than the Raptor for example