I'm not in Snohomish county so can't help much with what to monitor in the area. That depends on what you want to hear.
I have a BCD325P2 it is a good choice. I would recommend
ProScan for programming and controlling. It handles a lot of Uniden scanners and Bob the creator is very active in the forums. It has a 30 day trial that is fully functional. Here is the
ProScan forum. This along with your premium RR subscription is a good start.
It looks like most of the public safety is on a Motorola type 2 analog trunk system. Your radio should do very well with that system.
SERS
This user manual should help.
Easier to read BCD325P2 manual.
Good luck and take your time to read over and over again. If you need help there are plenty of people here with a lot of experience.