Welcome.
It may be fine to add nutrient now, it depends on your SG. Adding nutrient late can be risky because the yeast might not use it all up, leaving nitrogen hanging around to feed spoilage organisms. I don't use D47 any more but I recall it can be needy nutrient-wise, so if you SG isn't too low nutrients now might be a good idea. Generally not later than 1/2 sugar depletion, but I've done it as late as 2/3 sugar depletion without notable issues.
As
@bkisel said, for a few reasons, conventional wisdom is to let the wine ferment dry then stabilize with KMS and sorbate before back-sweetening (rather than trying to stop the fermentation). I don't normally do this until much later, after the wine has cleared. You will need to add some KMS (Campden tabs) after fermentation is complete, then roughly every 3 months while aging, more if you rack a lot.
You might need acid, might not, hard to say. You can measure pH and TA, but even before I had the equipment, I made acceptable wine by just using KMS every 3 months and adjusting acid to taste. Knowing pH and TA helps though because you can dial in the KMS additions, assure favorable environment for the yeast, and make adjustments prior to fermentation.
Also, most of us do most of our primary fermentation in an open bucket and move to carboy later, you can read up on pluses and minuses on that.
This is what I would do in rough order:
* take off the airlock and cover with a cheesecloth held by a rubber band
* get a hydrometer and measure your SG
* if SG above 1.040-ish add 1/2 dose of nutrient, not the full dose
* monitor fermentation until under 1.010 or so, then rack - on this rack don't try to keep it super clean, pulling over some sediment and yeast is probably fine, it will help the fermentation finish in the carboy
* after 7-10 days the fermentation should be completely done (as evidenced by SG under 1.000 and no change in SG for several days) so rack again and add KMS
* rack again at 30 days, then every 90 days
* the wine may clear on it's own, if so you don't need the SuperKleer; if the wine doesn't clear on its own or you are in a hurry, use SuperKleer as directed, then rack off of it after about a week
* stabilize by adding KMS, wait a day, add sorbate, wait a day, then backsweeten as needed
* watch for few days to be sure fermentation doesn't restart, then bottle.
There are many ways to skin a cat, others may offer perfectly acceptable alternative approaches.
