upgrading to SX 50

I have the SX 20 and Santa is bringing me the SX50. Santa is willing to bring me any accessories I'd use. I've read many threads on this forum and have found a grip I'm going to ask for.

I do use a polarizing filter with my 20, will I be able to use the same one?

Would a secondary flash to use instead of the pop up one be helpful?

Any other lenses or accessory recommendations?

I take my camera everywhere with me and take pix inside/outside/any place I can.

Thanks for any recommendations you can offer!