I have travelled a great e-distance seeking the wisdom of the Naghammer.
As my converting experience is limited to lopping an arm off an 80s miniature once upon a time in the 90s, I need some advice on a rather more ambitious project:
Creating the Avatar of Khaine (End Times: Khaine edition)


So, the plan is to chop up an old Eldar Avatar (Cheers to AGP for the one on the left!), and re-set it as a mounted character.
Then add Tyrion's sword, add a stylised shield, green stuff an upper torso, add a new Wood Elf head and hair ...et voila, my version of the Sword of Khaine-wielding Avatar!
As I have next to no experience in anything more difficult than kitbashing, I wanted to ask your advice on the main modelling:

The red lines are where I'm planning to cut, before reconstructing with green stuff and glue. Do you recommend that I pin all the new joints I'll be creating?
Also, regarding the Sword arm swap:

I would like to swap Tyrion's sword (centre) for the plastic lance on the right.
I would then like to put Tyrion's sword onto the Avatar arm on the left.
My question: what is the best cut to make? Across the wrist (red), or across the hands (blue).
I'd like the future Tyrion model (not necessarily this Avatar project) to be the gaming centrepiece, so I'd like the Tyrion arm + lance arm to be the most stable/aesthetic.
Thanks in advance for your attention.
All modelling advice including any recommended greenstuff and/or pinning tutorials appreciated
