Photek Softlighter II with Speedlite

I have a full-frame Canon EOS 6D camera with a 600EX-RT flash. I am seriously considering getting a Phototek Softlighter II, and I have a few questions:

1. I am looking at either the 60" ($95) or 46" ($75) sizes.  I would use it mostly with portraits of 1 to 3 people, but there are definitely times when I take group pictures of up to 20 people. Would I be better to get the 60" to use with the groups or would that be too big when I'm just shooting one person?

2. If I do get the 60" Softlighter, will my Canon 600EX-RT flash be powerful enough with the larger umbrella?

3. The strobist.com website recommends a LumoPro LP605 7ft. compact light stand and LumoPro LP633 umbrella Swivel w/ flash shoe adapter. Would this light stand/adaptor be sturdy enough to hold either the 60" or 46" Softlighter or would I need to buy something else?