Yes - that exhaust is the perfect size and it really is true to the M5 design DNA. It looks like what it should look like from the factory.
The stance looks very good. Your rear photo is the key one and you have taken it to close. You need to take it from further back and lower down so you can see where the tires disappear into the bodywork.
After you've driven it for a while, let us know about exhaust sound and whether you have any rubbing - especially on the front tires.
2014 ///M5 Individual Frozen Grey, Silverstone Full Merino, Piano Black, Exec Pkg, Drivers assistance plus, LED Pkg, Bang and Olufsen, 20" 343M Forged Alloy Wheels
Countermeasures: Bel StiR+, Laser Interceptor Quad HP, Zaon MRX
Upgrades: Eisenmann Sport with M Performance Carbon tips, Dinan anti-roll bars