As it turns out, you are probably in the good position where whatever you do should turn out O.K. You can have carbonated flat cider, uncarbonated sweet cider or any combination of these.
Just be aware that any unfermented sugar when you bottle will produce C02 and can lead to "bottle bombs" if there is too much sugar.
Don't add carbonation drops. They are simply a measured dose of sugar which will produce carbonation on top of any sugar in the cider when you bottle it. You may not need the amount of sugar in the drops (if any) to produce what you want. Typically, fully fermented mature cider at SG 1.000 will have no sugar so the drops provide the carbonation for fizz, but you can do this just by adding sugar (or unfermented juice).
This is a bit long-winded but now is probably a good time for you to get an understanding of carbonation. If you already know this, sorry, just ignore the rest.
A typical carbonation target for cider, beer, soft drink etc is 2.5 volumes of C02 (a volume of C02 in cider is the same volume as the beverage itself, i.e a litre of C02 absorbed into in a litre of cider is one volume). However, the carbonation target comprises two sources of C02. Firstly, when it is fully fermented the cider will have a volume of residual C02 in solution because of atmospheric pressure (only the absorbed C02 in excess of atmospheric pressure can escape solution). This residual C02 "off-gasses" and leaches out over time as the cider matures. For carbonation calculations it is usually assumed that there is between 0.5 and 1 volume in solution depending how long the cider has been sitting after fermentation is complete. We don't really know how much residual C02 there is but a common "split the difference" approach with relatively new cider is a guestimate of 0.8 volumes, however in your situation with freshly fermenting cider it is probably 1 volume.
Secondly, any unfermented sugar already in or added to the cider will be fermented into C02 by residual yeast (they just keep gobbling up the sugar until none is left). Sugar is fermented into 47% C02, 48% Alcohol and 5% new flavour compounds and the C02 is absorbed into solution if this happens in a sealed bottle because it can't go anywhere else.
So, the volume of C02 in a sealed bottle would be made up of the atmospheric pressure residual which doesn't contribute to fizz plus extra volumes from extra sugar that is added (called priming sugar) which creates the fizz. When the bottle is opened the C02 from the priming sugar escapes from solution as fizz until equilibrium is restored (i.e. the cider eventually ends up flat).
The rough rules of thumb for all of this are that fermenting two gravity points will generate one volume of C02 and similarly if working with the amount of sugar, a bit over 4 g/L will produce one volume of C02. It is common practice to bottle prime for carbonation by adding two teaspoons of sugar per litre, which produces a nice fizz
An example of how this might work is that I sometimes bottle at SG 1.010 (20g/L of sugar), let fermentation continue in the sealed bottle until the SG is 1.005 (how to assess this is another story). I then have generated extra volumes of C02 on top of the residual C02 but have 10g/L of sugar unfermented. If I pasteurise the cider to kill the remaining yeast (another story), I end up with a nicely carbonated cider containing 10g/L of unfermented sugar (which is about the same as 1/2 teaspoon of sugar in a cup of coffee).
By now your brain is probably spinning, but there isn't a "one size fits all" approach. You are in the situation where you can do any or all of the above.
I hope this helps. Have fun!
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