So you know what the SG was at start, test before adding more honey so you know how far its dropped, then test again after adding the extra honey. Record the numbers.
Then once its finished, measure it. You can then work out the total drop and logically the percentage alcohol.
To work out what levels of sweetness you like, you rack the finished brew onto sulphite and sorbate. I like to leave it for a day, then with a fifty fifty water honey syrup, I add a little bit, about a quarter pint, then stir gently before testing again and tasting. Once you get a level of sweetness you like (i like mine between 1.010 and 1.015) you can then think about getting it cleared, either time/naturally or with finings. Once its cleared then you can either bulk age it in a carboy or bottle it and age it that way (i do mine in bulk).
Leave it for at least 6 months before tasting.
Oh and don't forget, green/young meads often taste bloody horrible. And you'll be amazed in the changes that time brings to it. Making it a nice drinking experience.