Your cycle is doing well. Sounds like you have a good grasp on it.
You KH at 0 is a concern. It can lead to pH swings. Crushed coral or something with Carbonate in it will help that. Calcium carbonate is what I use to raise both my KH and GH.
As for your GH, that is about 15 degree GH which isn't that bad. I am actually extrememly suprised that your GH is so high and your KH is so low. Have seen it before but is still weird. I assume that the 300ppm GH is from your test strips right? Close enough either way but I wouldn't be too concerned about it. The only reason you would need to lower it is if the fish require softer water and most fish will adjust to your GH nicely. Just make sure to acclimate slowly just in case the LFS GH is a lot lower so you don't shock your fish.
I think that you can use either baking soda or baking powder, soda I think, to raise your KH but it will raise your GH also. 3dKH is considered the low side of safe for KH to help stabilize pH.
Also remember that large swings in KH and less so GH can actually be more harmful to your fish than pH swings. A small pH change suddenly will not be appreciated by the fish but small changes in GH and KH can be very detrimental, especially if the number are very low. Whatever you do to your KH, do it slowly. And remember to balance the water you are going to put in the tank before adding it if you are messing with the KH.
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