I just picked up a cx4 (takes 90 series mags) today from my  FFL.  It came with only one ten round mag so I am going to order some more mags.  Is there a reason to favor either the 15 or 17 round mags?  It looks like 15 round fits flush and 17 round sticks out a bit.  Also, I have seen some 90 series mags that have cut outs near the bottom of the mag, does it matter if They do or do not have the cut outs?  Sorry if this is not the best place to ask this question.

They CX4 setup for 92 mags will accept all full sized ones. You can run the 15, 17, or the extended ones like the 30 rounders.

Congrats on the new gun. They are really nice shooters. As far as mags go, I would get whatever you can now. 15,17,20 or 30 round mags are all good but make sure they are factory or MecGar- ( they are normally factory mags), as other brands like Promag are complete junk. The cut outs on the mags were for allowing debris-sand,dirt,etc., to fall out of the mag but if the mags don't have them, I wouldn't worry about it.

Thanks, I have ordered some actual Beretta mags and hope they arrive next week.  I have not shot the gun yet but I really like it.  The safety is a bit stiff but I assume it will loosen up.