Hi! Welcome to the forum and thank you for your questions!

1. Are you sure it is inserted in correct orientation (logo facing up, contacts down) ? It is a push-push mechanism with spring. First push locks it, second push ejects it. It is easy to do even with a door key or such. If the card is fully ejected it is just about aligned with the slot, and it should be easy to get it out with a knock on the case, and if not, then tweezers. The slot is too deep indeed which is unfortunate but it is already at the very edge of the board, it could not be any closer - as there are standoffs holding enclosure together, I did not see any other way. The idea is that you should not ever need to take the card out, it is mainly meant as a temporary memory space for some channels that work with larger chunks of sound (still work in progress), and as for the recordings, files will be downloadable over USB (this is not yet implemented in the current fw). Hope you can remove the card with tweezers - I believe there is no real problem as that slot would require a very strong force to cause any damage.
2. Blinking red LEDs indicate SD card problem - it is not communicating with the unit - as it is not inserted well. The type you mention should be 100% compatible.
3. By "bottom right-most single led" do you mean whie LEDs? They will react to sensors all the time. Status of inputs or delay is indicated by red LEDs,
as explained here - they may be blinking or steady, but the pattern should make it easy to recognize which settings is selected (once you learn which LED represents what - it's either numbers or L/R inputs, outer ones are mics, 2nd and 3rd and their mirror image is line in...)
If something does not behave accordingly it would help a lot if you could record a short video. Everything was tested, for example it is not even possible to program the firmware completely without the SD card working, and if you see all LEDs light up when you trigger sensors, that means they are working well. The board has a self-check, if you see blinking red LEDs after you power it on, that means something is wrong - but I believe that's not the case with your unit. There is a *very* small chance that during transport some element might get loose, so the hardware fault is not completely excluded but I'd be very surprised if that has happened.
4. You should not ever need to lower inputs, as there is AGC and various limiters. Rather the global volume is what helps to tame the sound

What's the problem exactly - does clipping occur? Which channel is it? The input volumes (if changed during play) are not remembered, however the output volume is. You can adjust input volumes via main menu too, then it will be remembered (all is explained in detail in the online manual as well).
Hope this helps - if you have further questions or need any advice I'm here

Cheers,
Mario