I do 25miles at least, 7.5 if going by train. Don't bother with a shower.
Just keep yourself clean and wash your cycling gear regularly.
8 miles isn't much, you could make up a hack bike for that. An old hardtail mountainbike, single speed, would do well.
Don't push the traffic - it just leads to accidents. 8 miles isn't going to take more than 30minutes for you, you're a much faster rider than me.