This question is three fold. I brewed a recipe yesterday that called for a yeast starter. My local HBS guy suggested that I use 2 liquid yeast packages instead as a simpler alternative. I chose to go that route.

Is this an acceptable way to get around using a starter? What are the downsides if any?

Next, I am still doing my primary fermentation in a plastic bucket w/ an airlock. The thought of 2 yeast packages brought to mind A LOT of yeast activity and the use of a blow off tube popped in my head. I shrugged it off and woke up this morning to a blow off mess on top of the bucket lid . Nothing major - just part of the fun.

Is it common to use a blow off tube when fermenting in a plastic bucket? Next, time I do a recipe like this I'll probably just go with a glass carboy and blow off tube.

Also, the CO2 blew all of my water out of my airlock and it was filled with krauzen when I checked this morning. I put water back into my airlock and it continued to bubble away vigorously.

What are the chance of any contamination having taken place?

i use plastic buckets for my primary fermenter all the time, easier for me to handle, and i just make sure i have plenty head space so i don't use a blow off tube. about the only time i use two packets of yeast is when my starting gravity is around 65 or higher, or when i'm not sure the yeast is viable. i used to have blow off messes when i used a carboy for a fermenter, but not now. if it blew it's lid it was still under pressure of co2 , so you should be alright.
gary

I've only had one foaming problem but that is not really a problem, a little messy but it won't hurt the beer. Are you making wine or beer?

My foam over was when I fermented my beer around 75f. Once I moved the beer to cooler temperature, I've not had any more foam overs. It is normal for fermenters to flip their lids and foam over. I also place the buckets in the shower if I am having problems with foam overs, it only last for a day or two at the most, then I can spray the mess down the drain. I believe you can find lids to fit the buckets that have a fitting for a hose connect to handle the foam over. Any time a lid comes off the fermenter, you run the risk of a contaminant entering the beer or wine, whichever you are making. I do not believe it would be enough contamination to ruin your beer. Alcohol and hops makes it difficult for contamination after fermenting. But if you get enough trash that falls in, it could ruin anything but the chances of the beer getting ruined because the lid comes off is pretty slim to none.

I just use the cork and airlock. I always start my yeast towards the end of the boil, about 20 minutes. At that time I add the dry yeast to warm water in a sterile bowl. I sprinkle the yeast on top of the water and let it rest. It will get all foamy on top and you will see some yeast settling to the bottom. This will help the yeast get started faster in the fermenter. After the wort has cooled to less than 100f, pour in the yeast into the bucket and stir it up. Put the lid and airlock on and it should start perking in no time. I do not use liquid yeast packs. I use dry yeast only, all grain or partial boil, depends on the beer.

More yeast costs more. I just use dry yeast and sprinkle it on top of the wort. Below 70 is a much better temp to add the yeast than 100 also. Go at least 80 or below. You will kill off some yeast still at 100.
Usually a 5 gallon batch of average % beer in a 6.5 gallon bucket will be fine with an airlock. That would give several inches of headspace. More wort will equal less space.
If in doubt a vinyl tube the size of the stopper will stuff into the bucket lid and work good.
I never do starters or use liquid yeast because i am lazy.