Help on correct Procedure Much appreciated

[jeff21up]

Hi All
Great to finally be a member and licence holder
I have just purchased a licence and was wondering what is the correct procedure for the following.

1. I want to install some themes.
2 I want to install some mods
3 I want to import my phpb2 forum using impex.
I understand impex only works on 3.6.0 so do i download 3.6.0 first and then install the themes and mods using those themes and mods available up to 3.6.0.
Do i then import phpbb2 using impex
Once i have done the above do i then upgrade to the latest vb release
If this is correct will everything be compatible (i.e the themes and mods) and finally once all that is done is the latest version backward compatible with prior releases of themes and mods.
Thank you in anticipation
Jeff