Personally I do think you could get away with a Liquidator, but I will not argue if it's a better choice. As you can see from my signature, my pool is around the same size as yours and I have successfully managed my pools' chlorine with a Liquidator for two full seasons (this is my third) here in the New England. In these two season I have never had an algae outbreak nor have I had to SLAM my pool. I have gone up to eight days between refills without problems and believe that I could have stretched it to 10 days if needed. I do use 12.5% chlorine which obviously helps with stretching out the time between refills. Fortunately I can get 12.5% for $2.99 a gallon which is the best value that I can find around here.
As for you questions, once I get the Liquidator dial in, I can go several days without testing, although I do try to test FC and ph daily. Generally I don't load up my liquidator unless I know that I will be gone for longer than a week, preferring to store my chlorine in the basement where it is relatively cool. So this means I added two or three gallons every 3 or 4 days.
I do have a single speed pump, so dialing in the feed rate is relatively simple. I'm sure a variable speed pump would be more of a challenge to dial in, although if there is a consistent daily run schedule then I believe it is doable. It's true that the feed rate will change with pump pressure changes, but I found that following the TFP method, my pump pressure doesn't really change that much. All you need to do is to monitor your FC regularly and adjust the flow rate accordingly.
So if we assume the 2 to 3 ppm daily FC loss rate that was suggested by Dave and 30k gallon pool, that would mean that you would need somewhere between 61 and 93 oz of 12.5% chlorine per day. Given this chlorine demand an eight gallon Liquidator could go 11 to 16 days without refill, although I would suggest that you stay to the lower side of this range. Now since you do have an auto cover, I would assume that your pool is covered while you are away and therefore without direct sunlight would hold FC better. This will result in your losses being closer to the 2 ppm, maybe even less and therefore making your two week vacation possible.
