1.
If the QRH doesnīt limit your alt, you can go higher. Your max alt will be limited by the gradually increasing Mach number when climbing with 300 kts. So just climb and watch your Mach and stay below the given limits. Continued flight will make only sence when on a short sector that takes you back to you favorite maint. facility. (again a 1000 other facts that will make you decide different, avaiton is unpredictable)
2.
You have no alt limit. Watch your cab alt indicator and decide. Lots of contributing factors there. I had a dispatched flight with one pack inop and went in FL 250 from Germany to HEGN. On the way back we had so nasty CB weather over the alps, that I climbed for a short time to FL340 to get above. Itīs always a bargain. If it happens enrout and you are high, if the second pack fails you will have a gradual loss of pressure since the out flow valve will close, so no need for hectic. Just watch the cab and diff press indicator and arrange your descent accordingly. There is no need to leave your cruising FL.
3.
Too many contributing factors, so donīt concentrate on one solution.
Take all available facts into your decision making process like:
How many pax, what country, how good is their english, can the tower see the A/C, whatīs the WX, is the fire brigade next to the A/C, who is my purser
Hope it helps
Repulo