Here is the link to the thing I am looking at getting for a steal, like $20 nearly-new. LINK I know the quality is so so w/ the brand, but I'm not too worried about it right now I guess. I'm  content w/ simple front & back coverage for now.  THeoretically later I might like to get a high quality interceptor type vest or whatever.  

Planning on running mostly chest rigs.  Maybe sometimes I'll just throw the chest rig on over this getup.  I'll probably also get some concealable soft armor & can wear concealed or under a rig or under a rig & a plate carrier.  

My main question is:
if I get some decent plates to put in this carrier for now would they fit in a nicer plate carrier in the future?   I would be interested in probably steel plates that can stop regular AK47 ammo.  I think that would be level 3?  

I've got one of these that I picked up for $20 on fleabay.  I got it because it came with a lot of nice molle gear included.  It is not very good.  Not comfortable, overall a piece of crap.  I also have one of the new Condor QPC carriers.  Much better.  But, to answer your question, it takes standard 10x12" plates, so yes plates that you purchase for this carrier will fit a better one later.  Also, steel plates=HEAVY!  I just got in some 8x8 steel LVL 3 plates I picked up off the forum, they weigh more than my whole QPC plate carrier with soft armor, ceramic plates, and ammo on it.  I've just got some old LVL 2 soft panels in that older super cheap Condor carrier.  More than anything it's just a "chest rig" for me.  Got mag shingles on it and can wear it to the range.  Little soft armor in case something bad happens.  It would not be comfortable at all with steel plates.

Yeah, this would be just something to put on for very limited circumstances of short duration.  It is 20 delivered, in black.  I think I'll get it so I have something to wear plates sooner than later.

That is pretty cool that that other condor vest you have is workign out so well.  Those are like $80 right?  Does that one take side plates?  How much would a similar design vest cost for a top shelf USA made one of "milspec" quality or better?

No built-in pockets for side plates.  I got it included with a set of ceramic SAPI plates so I can't really comment on how much it cost.  I haven't done much research yet on better plate carriers.  I've seen Eagle stuff for under $200.  I'm just a keyboard commando and wanted the plates for an upcoming rifle class/zombies/whatever.....

I know there was another post on here where the individual  had to modify the front top to make it curved for comfort.  That straight top pushed up into the neck area.