To hang out, the reef may be the right size, but you really should think about it. We originally thought to have our reef larger but then cut it in half so as to have a clear swimming area (a lane if you will) from end to end... BUT, since you're using the deep end as a swimming area with the swim jet, that may not be an issue. I personally have not, but have you used a swim jet before? Just asking as I'd hate to get one and then realize that you don't like it etc...
One thing I would consider is your vertical descent, with it positioned as now, are you able to sit and let it spill onto you? Again, comes to personal preference but some people think it's nice to be able to sit under the waterfall etc... might think about moving/ widening it maybe?
I like that your spa is nice and large (ours is 7 x 9)... I figure that if you want a spa, get a spa and make it good sized... no need to cramp up into a little circle, have something people can comfortably relax and lounge around in. Our spa is raised ~7.5'' or so (one step) from the patio (~4ft from the pool) and we think the little coping step around the spa from the patio looks great.
Planning is fun!