1) [KNF] sieged a base for about 7 hours until it was finally down. And we did that with -a lot- of ships. We had to fend off defenders multiple times when they used various ships - from trying to suicide supply it, to an Outcast bomber swarm, and in the between combined attack by K'hara cruiser and Outcast cruiser.
Any base with supplies can stand more than 2 hours.
2) Just so you know that 5,000 units of BA can repair 200 million hull points. Yeah, that much. Given the fact that the base repair rather quickly any well supplied base, even level 1, can stand a siege for long time.
EDIT on (2):
That's with only 1 type of commodity to repair the base by the way. If you have 3 types, the base is about immortal.
3) I am sorry, but either that the second attack on Brimestone was done with abused bug, or it was simply not supplied. I tend to go for option number 2, given the fact that it was stated that the base hull was dropping rather slowly, and it took 2 hours to take it down. A bug would take much much less.
EDIT on (3): If the Valor had a way to bypass the shields, it would tear the base apart in minutes, even if it had all types of commodities and enough to heal 90 billion of HP. Valor DPS is simply larger than the repair's, but with shields - No way.