i have read a couple places that you really don't even need a turbo timer because the WRX's turbo is water cooled it cools itself down after the car is shut down. turbo timers, i've read, are mainly for oil cooled turbos, but it's definately not going to hurt it. i have a turbo timer on my 02 wrx.
yes the bov will dump if you just rev it up. the loudness just kind of depends on which bov you get. i have a blitz bov and that's pretty loud.
as for a boost controller, i started looking at those when i first bought my WRX, and the more i've read the more they don't sound as safe as reflashing your ECU or getting the Cobb AccessPORT. manual boost controllers work but you have to be careful with them because the tend to produce turbo creep and that's bad. most electronic boost controllers can regulate that turbo creep. and definately get a boost gauge, if you get a boost controller, or even if you're changing anything with your boost. i've read a few places that 15.5 - 16 is pretty much the max you would want to go with the stock turbo. you can get a bigger turbo and run more with other mods, but i think that's a little more than you're thinking about doing. am i right?
i would go with the Cobb AccessPort. that thing is awesome performance wise, seems really safe, won't void your warranty because you can put your settings back to stock, and Cobb tunes all Subaru so they know what they're doing.
well anyway, i hope this info. has been helpful.