Did you try to see if a pipe would fit inside the rough-in valve? Many of them are dual purpose, screw on a female fitting or solder in the pipe directly.
Soldering that close to a threaded connection is not going to give you a reliable connection.
As to the spout, many of the Grohe stuff specifies a twin-el with the tub spout (if the valve doesn't have a diverter in it). Failure to use one when called for can lead to problems. That may change how you want to hook things up.
Can you make your first connections to the valve THEN mount it in the wall? You really shouldn't solder close to a threaded connection.
It would be preferable to not use a Sharkbite there, but they are approved for that application. They also cost probably 10x as much as a solder fitting. If you don't prep the pipe end properly, you can damage the O-ring seal, but if done right, they work. Since they will swivel, you have to anchor the rough-in separately, you can't do it on the pipes.