First impressions on Casio FX-5800P

[Ask Mait]

Hi folks, I am a new member and it is my first post.
I 've been with Scientific calcs. for over 30 years and mostly they were fx-82s. Have been using 35s since 2009 and learning to use RPN was really a challenge.
Today, I am considering getting the fx-5800P, did most of the online research I could but still have at least three questions. Hoping somebody would take his time replying to.

1) is fx-5800P the latest and the best from Casio programming ? as I also saw fx-4500, 3650 and 50 on their website?
2) Comparing the keyboard of 5800 with those of fx-82 and even HP-35s, I could not find a dedicated key for sign change (+/-). This would be important key to me, does is it take long to do without it ?
3) the last-but-one key on the bottom right (-), what is it for?

I understand my queries could be foolish, my apologies and sincere thanks in advance.

Thanks
AJ