Staggered sugar source addition: before or after racking?

I am currently set up to use a modified recipe for a sparkling oaked acerglyn with the following adjustments:

• Reddit user Balathustrius's SNA schedule using Fermaid K, Fermaid O, and DAP
• Additional honey added to the must prior to pitching
• A bourbon soak to sanitize the oak spiral
• 1 gallon of apple cider added at some point during primary or secondary
• Lalvin 71B yeast, which has an ABV tolerance of 14%

Having analyzed the sugar content of the dark robust maple syrup, I found that the must would initially (based on step 2) have a relatively low specific gravity and might turn out somewhat dry. However, the recipe also calls for staggered addition of the maple syrup one week prior to racking. Would this second syrup installment be sufficient to somewhat back-sweeten the mead or would it trigger secondary fermentation and continue to be fermented into alcohol? I'm assuming since the maple syrup wouldn't appreciably change the volume of the must, the must is already approaching peak ABV and wouldn't change much despite the addition of sugar. However, I really, really want this recipe to be at least semi-sweet. Should I add more honey to the must initially or will the collective maple syrup / apple cider additions do the trick?

That said, when it comes to adding the apple cider, should I do this before (i.e., at the same time as the second syrup installment) or after racking? I have heard that in racking and ditching the collection of lee at the base of the carboy, 90-95% of the original yeast population is being removed. I fear that adding apple cider will heavily dilute the alcohol in solution without fermenting much if done so after racking. I don't mind some dilution, but by adding a gallon of apple cider the ABV could dive from 14% to 11.6% which I would ideally like to avoid.

Finally, I would like to retain the sparkling aspect of this recipe. How long should I wait after the addition of the apple cider before pitching the corn sugar and bottling? Trying to avoid any bottle bombs if at all possible.

EDIT: Considering the already diverse flavor profile, I don't want to smother the finer notes with cider. How much cider is too much for a five gallon batch? Could I carbonate it using the cider alone?