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> 1.) Some of my wines are astringent to the tongue. Specifically to the
> edges of the tongue, if that makes a difference. ...
Astringency on the front of the tongue is associated with acidity. Astringency on the sides of the tongue is from tannins. If you are adding no tannin, then I suggest cutting back on skin contact (press earlier), aging your wine longer, or decanting in advance of serving.
2.) With white wines, I have been having a problem maintaining SO2 levels.
> My wine always seems to oxidize - get a brownish tint to it. ...
What grapes are you using? Some native American grapes are known to produce wine that oxidizes easily. Jack Keller wrote about one on his site but at the moment I can't find the reference. If proper SO2 levels aren't working for you, perhaps you should consider using an inert gas when racking. Also double check all of your airlocks and bungs; make sure everything is airtight. On the off chance that you are aging in oak barrels, you should consider switching to carboys in order to avoid the micro-oxygenation that occurs with barrels.
3.) I will be planting Vidal Blanc grapes in the Spring. 1 acre of them,
I wish I had an acre of anything :-}
Greg G.