I recommend buying your software one piece at a time. After you get Poser 4.0, play with it to see what it does do and what it doesn't do for you. Then you know what else you need to buy.

Michael 2.0 and Victoria 2.0, from DAZ3D, are extremely popular figures, and those are probably the only two other Poser 4 products that you could almost certainly buy right away and be certain you're not buying something you don't need.

You will also find that you will need paint or photo software to touch up your renders. I use Adobe Photoshop, and I think the other popular one is Paint Shop Pro. Those two have lots of tutorials written for them, so they are good choices. I can also add from experience, that Corel Draw is completely inadequate to touch-up renders.

Get everything else you want on a buy-as-you-need basis. If you have a fast connection, almost every piece of additional software you want can be bought for immediate download.

And, of course, only buy it if you can't find it for free first. There's just lots of good, quality free stuff available. Always search free stuff sections first.