For home portraits, just pick up some cheap scoop lights from your local
hardware store (Lowes/Home Depot or privately owned).  They cost around
$5-10 each, use normal household bulbs and have grips so you can mount
them anywhere.   I got the term "scoop lights" from a friend, these are
just pieces of tin with a place for the bulb and a strong grip.

With 3 of those and maybe a reflector, you can do a lot for only a
fraction of the cost of buying new strobes.  Yes, they are tungsten, so
just set your white balance to compensate.

I use them in my finished basement. It has drop-down tile ceilings about
7 feet high, so it's great for sitting portraits and headshots. I run
the extension cords through the ceiling and grip the lights to the grid
holding the ceiling tiles.

Yep.

Although I don't know why you'd want more than one 550EX & one or two
420EXes.

yes.

what I do a lot is take the flash and bounce it off a sidewall for an effect
like a large softbox, use a reflector, that should get you going.   use some
of the money you just saved by buying a decent tripod.

I'd use 3 of the 550EX lights. All you need to do, is set 2 of them as slaves.
Use white umbrellas if you don't have a a white celling to bounce off.

Fred