I've got similar questions. I'll be doing my first hefe this weekend. Due to an out of stock of Wyeast 3068, I'll use one smack pack of 3068 and one tube of WLP300. With concerns about excessive blowoff, I was thinking about splitting my 10 gallons into 3 carbouys (5 gallon carboys).
Since I'd like to compare the differences between the yeasts, now I'd be up to 4 carboys, which I could still do.
Is the blowoff really excessive and worth the trouble? If it saves me a 1/2 gallon of beer, it'd be worth it to me.
Also, with so much yeast suspended, is it worth harvesting?