The difference in height is actually 1cm, not just 5mm.
Anyway that difference will not be enough to make your car bump anything on the road, provided your car is still using standard suspension/not using lowering kit suspension. The effect is slightly firmer ride, and less accurate speedo & odometer reading (the actual speed & mileage will be slightly lower than shown). There'll be very minimal improvement in pick up but mostly unnoticeable.

It will make your car accelerate just a tiny bit quicker but your actual speed will be a little bit lower than the speedo reading.

Yes it will, especially to 215/50 since it will add 1cm to the sidewall thickness. For me, in general I won't use anything thinner than 10cm of sidewall as they already starting to be harsh. 215/45 is only 9.7cm sidewall while 215/50 is 10.75cm and 205/50 is 10.25cm.

But keep in mind that people do have different perception/feel about comfort. Some can tolerate very harsh ride and can still claim his/her setup as comfortable. Some have even less tolerance than me, hence will say my rides are already harsh. So the 10cm barrier is just for my personal preference, may not necessarily be yours though.