So finally to the questions, if anyone is still reading.
1) I topped the barrel off to the tippy top, till beer started to overflow a bit. Is this right? do I want any air space? as I sample (not often) should I re-top off?
2) I am planning to let this ride for another 4 months so the original almanac brew will be 6 months old, draw off 2-3 gallons and replace with something similar. Does this seem right? after than I will go with a 6 - 12 month cycle until I am totally sick of it or the barrel goes way way south.
1. Since the beer is already fermented there is no risk that the beer will overflow out of the barrel and spill everywhere, so you want it as full as you can to minimize air contact and maximize the amount of beer you can take back out. If it is that full you don't need to top off when you take a sample unless you are sampling frequently or taking an excessive amount. You really don't need to take hydrometer samples because your saison is going to dry out in a matter of months and you're just looking for it to reach a desirable flavor profile. That only takes an ounce or so to taste. You don't want to break open the pellicle constantly to taste it, so even those samples should be infrequent.
2. It's a fine plan going in but you should let the flavor profile guide when it is time to pull beer and replace it. You may not like the flavor profile after four months, it may be ropy, etc. On the other hand, you may like the flavor of the beer at a younger state, in which case you may want to pull and refill every 4-6 months.