[Nexus 7 Q&A, Help & Troubleshooting] bftb0:
@OP

The recovery you describe is the stock recovery. If you used an OTA process after rooting, probably that is what overwrote the CWM install you did previously - so that explains why you see what you do when you boot to recovery via the bootloader menu.

When you use the "reset by holding the power button down for 30 seconds" you are crashed the running OS and potentially corrupted any filesystems which are mounted "rw" (read-write). So, that might explain the bootloops that occurred thereafter.

You have a couple options, but before you try any of them, I would suggest that you observe the "power state animation" that occurs for about 10 seconds when you plug the tablet in to the charger with the tablet turned off: it shows you graphically how much charged the battery has. If the animation starts with a nearly all black battery, and then "fills up", the battery is still deeply discharged; if it is all white, or mostly all white, and the animation only "tops off" the battery, it has a good charge.

If that animation shows a battery which is still discharged, I would try to solve that problem before doing anything further. It was a low battery condition that got you into trouble in the first place; no point in making things even worse.

OK. Well, if you weren't a toolkit user, I would suggest a couple things that could be done manually using a custom recovery to attempt a repair of the /data filesystem, or rescuing your raw data for a later data recovery effort. But they involve command-line stuff, so me mentioning it is a waste of time. Suffice it to say that if you still have an unlocked bootloader and functioning drivers on your PC, you can re-install whatever custom recovery you want (using either fastboot or Wugfresh) and then use the capabilities of that custom recovery. Given that you didn't even realize that your custom recovery went missing until now, that's probably also a waste of time too - I probably can safely assume you don't know what its' full capabilities are.

So, flash a custom recovery and perform a reformat of the userdata partition ("Wipe Data" in TWRP, don't know what it is in CWM). You could even try taking a Nandroid backup before doing this, but the problem with doing this is that by default it will try writing to /data - so under the presumption that your userdata partition is hosed up, writing a whole lot of stuff to it (the backup) may not create a reliable backup image(s). With TWRP you could write backups to an external device, though.

That leaves a factory reset. If you do it with the stock recovery (simultaneously press power and vol-up for about 1 second after the recovery splash screen shows up to get the menu), it will erase EVERYTHING in the /data partition - including your everything in the psuedo-SD card.

Without any further learning on your part (abandonment of toolkits), it seems like the stock recovery factory reset is the least-effort solution for you. As I said, this will destroy ALL of your data on the device, but your device should return to a bootable condition. If you made any Nandroid backups and got them off the tablet, you could restore them after installing the custom recovery which made those same backups.

good luck