Welcome back, and yes, it is good to do some research before investing.

For Poser, V4 is still the queen, and she sits pretty solid on her throne.

The Gen 2 figures are best left where they belong, DS.

Why?
Poser8, and Poser9, and Poser 10 are 32 bit applications, so you are limited in available RAM of 2GB per app.
You have to upgrade to a Pro version to get a 64 bit app.

Fiddling with DSON to get a Gen 2 figure to work in Poser, (asuming you have hair and wanna get bold), it will be gone after you got any Gen2 figure to work in Poser.

Some get lucky, most give up. And then the whole thing starts over for ANY clothing, shoe's, hair, you name it.
RAM and CPU go downhill fast.
And mostly it takes from minutes, to a full coffee breack, just to get the things loaded.

There are TON's and TON's of posts here about DSON, V5, V6. .

Long answer  : read them all. (See ya in a year or 2 LOL.)
Short answer : leave them in DS.

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So V4 and M4 are still your best option, certainly when you have a ton of content for them, and new stuff gets build every day.

YES ! When upgrading Poser you can link your existing runtimes into the library of your newer Poser version.
And you can organise then as you like.

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Happy Posering, Tony

Poser 1, 2, 3, 4, 5, 7, P8 and PPro2010, P9 and PP2012, P10 and PP2014 Game Dev
"Do not drive faster then your angel can fly"!