Hi- I'm back!
When it comes to light modifiers you really can't have too many. Not every box or umbrella with accommodate every job. The big boxes make good fill lights- mounted high and in back of the camera the can provide an even fixed fill light for preserving shadow detail in your images. The thing to remember is that big soft boxes and giant umbrellas will not enable as much precise control as their smaller counterparts. It's OK to mask off part of a big soft box (good idea) but the unit will not be as nimble as a smaller one and could ,in certain cases, become a bit cumbersome.
There is no reason why you can't use your big box as a fill source and use a small inexpensive umbrella as your main. I prefer a smaller main light myself because I like a bit more contrast and I move my main light around quite a bit in order to correct for facial features and adjust my lighting pattern precisely as I like it.
The more powerful ABs are a good choice- it's good to have additional power when you need to increase your depth of field or if decide to take on some commercial assignments where smaller apertures are needed. In portraiture a problem occurs when you can't reduce the power output enough to create shallow depth of field. Many traditional portraitists prefer to throw their backgrounds out of focus. I think you have made good choices for a starting kit for portraiture with electronic flash. Paul Buff has been producing professional lighting equipment for a long time now- it is simple, well made and durable. If any of the light modifiers are not satisfactory you can exchange them- can't ask for better than that.
Stop worrying
- you have good gear on the way. The most important thing in good portraiture is your technique. You will need to get used to your new gear and practice and experiment with it- that's half the fun. It's like driving- you need to control the equipment- it does not control you. The old story goes that a good photographer can make great photographs with a candle and a pin-hole camera. A lazy photographer can have all the gear in the world and be unsuccessful.
I am not and I don't encourage photographers to become "gear-heads", those are folks who think that the equipment makes the photographs when actually it is the PHOTOGRAPHER who makes the images. On the other hand, investing in good equipment is wise. You don't want to waste money on junk and then make another purchase shortly thereafter to replace gear that simply does not do the job. When you work with good gear that you can depend on, you have more time to concentrate on your posing, lighting and attention to detail rather than fumbling with stuff that gets in your way.
All the best in your new ventures- keep us posted! Ed