I can only answer #3, I personally don't use ketostix because I know I'm in ketosis if my carbs are under 20 and they would give me something more to obsess about.

#1 Personally, I plan to eat keto/low carb as my lifestyle for the rest of my life. I get my carbs from green vegetables, nuts (peanut butter) and chocolate, mainly. I'm healthiest eating this way and I want to eat healthy for life, so that's my plan.

#2 Just brush often.

#3 I think keto sticks can be helpful when you are first starting out as an indicator, but they are not necessary or entirely accurate. If you really want to know, get a blood glucose meter. That said, I have the meter at home and have never gotten around to using it and I no longer use the sticks. After a while, you can really tell when you are in ketosis by the way you feel, your energy level, etc.

#4 I won't get into all the science of it because you can Google that, but in keto your body will be dumping a lot of sodium/potassium/magnesium. I purchase high-quality sea salts (not all salt is created equally) and put it on as many meals as possible. If you get a headache a few days in, chances are good you need more salt; when that happens to me, I actually take salt shooters to get my levels up. Also good to take potassium and magnesium supplements as you'll likely not be able to get enough from foods. Additionally, I personally take Cod Liver Oil for its health benefits.

I guess I would also mention that it's cool you have been eating paleo. I see some people do "keto" but it's all from fast food, processed junk, which I personally don't believe is healthy. I eat pretty close to paleo/primal, except I have dairy in the form of cream cheese, heavy whipping cream, grass-fed butter and some cheese (and I'm cool with that because it's high-quality dairy and it agrees with me).