Welcome! The F is the way to go...as a weekender or a daily. To answer yoru questions..
1) When I first got to drive this car on the streets in "F" Manual mode and SPORT vdim settings, I inadvertently found myself looking to press down the clutch when I got to redline. You'll be surprised how direct and the paddle shift (or the gear shift if you wish) feels when rowing through the gears.
2) Nope, the gearshifts in regular drive mode are very seamless. All the magazines and such complain about having too many gears, but having that 8th gear is crucial while cruisin on the freeway. Fuel economy with the higher gears are key.
3) That's middle row seat in the back is pretty useless in the IS, even with having a formal seat in the middle. If you really have to squeeze a 5th person, just have the person sit on a thin cushion and stay very still.
You definitely should drive it and experience first hand. We can tell you all the pros and cons, but ultimately in the end, it's how the experience pleases you.
