Hello all.
I suggest consider consultancy from one of the experienced companies, Temenos itself or one of its partners.
I was part of an upgrade team from R5 to R9, and the previous steps involved about 3 months of business and technical work. The upgrade itself required about one month, starting from software installation, user acceptance testing (UAT), issue tracking, parallel between R5 and R9 and go live in R9.
Best regards from Mexico.