The pickups are easy DIY if you have a soldering iron (e.g., 40W) and some 60/40 solder.
If you have passive wiring now (which I suspect is the case with this model, I have fixed up a friend's pickups in a Viper-50) you can retain that. I guess what I am advising against is piecemeal upgrades of the harness. I would get a whole new harness made rather than upgrade the original one bit-by-bit, and just keep the original one in case you ever want to revert. But if the pots are 500K pots then you should be able to get a decent sound out of it. The issue is more with Gibsons and Epiphones with their 300K pots and odd PCB wiring set-ups, or higher-end LTDs with EMGs etc.
Personally I would just do the pickup change myself and then take it to a tech to do a standard setup, check everything over, setup the tremelo, etc. It will save you a few bucks and you'll learn something. Just keep an eye out for the pickup springs, don't lose them! You unsolder the pickup wires from the harness in the control cavity and then take out the pickups with the pickup rings. There are wiring diagrams on the BKP site. I'd have a look at the pickups first but I'm guessing you want 53mm short leg 4-conductor.
Have a look at this video for some idea of how pickups come out etc.
https://www.youtube.com/watch?v=W9iyaf46r5AIn terms of the choice of Juggernauts that would depend on your guitar's woods, construction, the style you want to play, etc. Without knowing more I wouldn't say much but Juggs could be a safe bet