Quote - 1).I Assume I get a genesis "base"model free with DS

what do I need to get a "Fully morphing" genesis Male& Female?

There actually are two different version of genesis.  The original Genesis, now sometimes called Genesis 1,  is a single base figure that morphs into both male and female versions.  Genesis 2 has separate male and female base figures.  You get the both the Genesis 1 and 2 base figures free with DAZ 4.x.

To do much with Genesis 1 you need the "Genesis Evolution: Morph Bundle". That contains both the head and body morphs.

To do much with Genesis 2 you need the "Genesis 2 Female(s) Morphs Bundle" and "Genesis 2 Male Morphs Bundle".  The bundles include both the head and body morphs.

There are other specialized morph bundles too, but those ones are required for lots of characters.

Most new products coming out today are for Genesis 2, except for some creatures on Genesis 1.

Quote - 2). I have some old V4 morphs ++ figure face morphs that I like.
will I have to recreate them from scratch  with genesis?

You will still be able to use V4 figures in DAZ 4.x. She still works fine.

You can transfer the body/head shape to Genesis 1 or 2 with "Gen X". The V4 skins will work on Genesis 1 with no change. For Genesis 2 you will need "Victoria 4 for Genesis 2 Female" to use the skin mats on genesis 2. You will also need to change them into DUF format, which you can do by applying them to Victoria 4 and saving them as a material preset.

But you don't need to transfer anything. You can just use Victoria 4.2 in DS.

Quote - 3). Am I correct in assuming that any really old Daz Figures such as Mike 2 will not be able to be opened in DS 4.x even if saved as a DS scene from my old version of DS 2.3??

I'm not sure about this. Don't have any really old figures or scenes saved in really old versions.