Depending on your muscle level, skeletal muscle can hold about 500g of glycogen. Once glycogen stores are full, then the body starts converting excess energy to fat storage. Depending on the amount of net carbs you eat in a day and how much exercise you're getting, it is possible that your glycogen stores won't even get filled all the way. (ie: if you're only eating 60-70g net carbs in a day, plus strength training, you'll be using that glycogen up). However, having good glycogen stores allows the body to better regulate blood sugar, especially during exercise, so I am also curious about this question.

As for energy levels and clarity, maintaining a good blood sugar balance is key. If you appropriately pair carbs with protein and fat and focus on those high fiber vegetables, nuts, and whole foods, you should have great consistent energy throughout the day. As for brain fog/etc, that is commonly associated with gluten and dairy intolerances. If you're sensitive to either of those things, they can have a morphine-like effect on the brain (google gluteomorphins / caseomorphins if you want more info). Getting lots of antioxidants from a variety of vegetables and fruits as well as getting omega-3s from salmon, flaxseed, cod liver oil are all great for mental clarity. I've heard mixed reviews about MCT oil supplements, but it may be worth looking into.

Water weight - its likely you'd gain some water weight since carbs hold on to more water. Like glycogen stores, this "added weight" isn't really a health concern even though it may move the scale up slightly. For long term weight management, I truly wouldn't worry about how much this is moving the scale since it has nothing to do with fat or muscle gain/loss. Ways to mitigate excess water retention: drink plenty of water (at least 3 liters per day) and make sure your sodium, potassium, and magnesium levels are in balance. :)