I have one girl in a viv and my boy in a a tub and I personally prefer the tub. The viv is more aesthetically pleasing but I find I have less issues in my tub with feeding, handling, stress, humidity etc and I honestly believe they are more secure. My boy is 700g and in a tub but unfortunately I don't know the capacity as he came in it when I bought him.

I agree with Mootworm, I find that humidity keeps much better in my tub and the temperature is easier to monitor.

For security I would suggest the tub although affixing a stronger top to your tank would also work. It comes down to your personal preference
Cats can be quite sneaky (not an owner of any myself) so I understand your issue and the stress it could be causing you BP.

Good luck in creating your cat-proof environment!