I'll take a shot at this. I started with plastic buckets, had four glass carboys at one time and now do all my fermentation, clearing and serving in SS cornys, except for stuff that needs to sit a real long time still gets bottled.
Don't buy any more plastic, plastic sucks. It is cheap, and works good for a while, but once your bucket has a scratch you'll never get the bugs out of the scratch. It is OK to have one or two around to use for other things.
Glass kicks butt as a fermenter. It isn't temperature tolerant, and the handles are NFG, but you don't have to worry about oxygen permeability and you can see what is going on in there. Glass is very difficult to scratch while cleaning and very easy to disinfect as well. Keep one 5gal going with EW's Afelwine, keep the six gal you got as a primary and replace your other two 5gal glass with two more cornies as you can afford it. If you are remotely interested in meads, keep the "other" two 5 gal glass so you can rack your mead back and forth.
Now that you are kegging anyway, look at conditioning and eventually fermenting in cornies. wortmonger has a thread going in the general techniques section. the title has to do with running your primamry ferment under pressure so your session beer carbs as it ferments, but you could put an open hose end on a grey post, open end under water and bang, you have a fermenter.
Along the way you could primary in glass while conditioning/ priming in kegs.
Having searched a lot of threads lately, I will say that if you are going to bottle "some" of a batch for shipment or sharing, you might as well *I am expressing an opinion* bottle the whole batch. There are a few folks here counter pressure filling bottles with consistently good results, but not everyone.
M2c
EDIT: I gave all of my glass to my brother in law the wine maker about 12hours ago. I don't miss it. I now have one kind of container in my brewery. I got 5 gallon cornies. They are either clean and topped with CO2, or clean and full of 'something', or they need to be cleaned. They all get cleaned the same way, with the same chemicals yada, yada, I am in hog heaven.