I'm no expert but I think you will be fine. I have a apfelwein thats at 9% and .996 with Montrachet thats been sitting in the primary since January and it hasn't seemed to effect anything or have any sulpher tastes.
If you keep adding sugar, you'll still have a ton of lees and a wide headspace. I'd invest in a carboy, buy some jug wine, apple cider or something that comes in jugs, etc. You really need to rack off of the lees and reduce headspace.
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