As other said, go the speed of the field. Crashes happen when people try to go faster/slower than others through turns. And watch out for that one guy who will dive bomb the corners even if he doesn't have the line - there's always at least one person in a Cat 5 field who does that. It's okay to leave a little space as you enter into a corner, but don't be surprised if someone takes it.
Read up on some of the other threads and stickies on racing. Crits are less about FTP and more about dealing with surges - How many times can you sprint out of a turn before you run out of matches? It's not uncommon for Cat 5 fields to blow up in the first few laps. Someone usually tries to win from the gun while someone else - usually at the front - can't get clipped in.The first few minutes will be fast, then people will start to fade and things will settle some. If you can make it through the first 5-10 min, you should be fine until the end. If you get dropped, just keep going and ride safely. That could mean slowing on a straight so that the field doesn't catch you in a turn.
As far as tapering this week, I think you should maintain your training intensity, but decrease the volume. So, if you normally do 6 sprints on Tuesday, only do 3 the week of.