To be honest, it's fixable but for the issues you have, I'd also suggest just getting a new tank.
If you want to try and fix:
If the crack is just at the top, it could be filled in with some silicone to prevent cuts when you are working on the tank. If the crack also goes down the side some, I would silicone a glass patch on the inside of the tank. You make the patch larger than the cracked area so that the stronger parts of the glass are part of the fix.
The bubbles within the silicone at the bottom of the tank could just be air pockets that you won't see when the tank is empty. As long as they don't leak, they shouldn't be a problem but they can be unsightly. The long stretches of missing silicone ( in pic 3) are a bit concerning. There would need to be more pics at different angles to determine if they are a serious problem or potentially a problem down the road.
On a side note, the silicone work looks like it was a repair at some point and not a manufacturer's workmanship which would make me hesitate on using the tank in an area that can't handle a water leak. If it's a manufacturer's work, I'd use a different brand.
Hope this helps.