Nmuta,
Since you are familar with Max let me just say that rigging a character for Poser is totally different from Max, different program differnt ways. Bones are bones but Poser is a different species.
There are programs available that are supposed to take a riggerd character from Poser and bring it into Max without hardship...but I am not convinced that there isn't a good deal of tweaking afterwards. However, I have not tried the other programs...just heard from others.
Sure you can do what you are asking, frog head on mans body, creating armour and clothing for Poser, etc. You are ahead of the game in that you know Max and are familiar with modeling ways. But you will have to learn a new program and it's ways...Poser.

You need to  learn Poser's body part terminology and it's parent/child relationships. The brains of any figure is it's CR2 file....learn to hack it. (you will have to search high and low for good tutorials that won't leave you hanging) When you model clothes take the obj from the Poser runtime folder, don't export from Poser. Some peps do (export from Poser)...I would encourage you to not. It gets funky.
Learn how to create a blank CR2 and hijack that for your custom figures. Some of your programs of choice will be CR2 editor, obj action scaler, ZBrush, AutoGroupEditor and of course almost any program from Phil C (google), also a new one for me (though it's very old) PHI builder.
For me, if it's a suit of armour and/or a custom humanoid character...hijack a CR2. If you are creating multi limbed beasts of prey...PHI builder. Though it is different to learn, once you do it's rather easy. Some just use PHI builder and nothing else. Nothing wrong with that.
You'll find some threads in Max and ZBrush forums about interaction with Poser...just don't tell anyone you are using Poser...almost an automatic blackmail in some places.
Good luck.

Comitted to excellence through art.