If you've never done ketosis, you are missing out. IMO, It is, hands down, THE most effective way to burn fat while sparing muscle, that being said, it has its drawbacks.
Drawback #1 - Working out loses all its flavor. Everything is a struggle in the gym and it pretty much takes all the joy out of working out. Training is tough even with a targeted ketogenic diet where pre and post workout carbs are allowed.
#2 - You will miss carbs.
#3 - You will not want to eat, will have zero appetite.
#4 - Leaves me feeling foggy and emotionally flat especially in the beginning.
That being said it is very effective, even for short periods of time. I'm ectomorphic but I do have some stubborn fat around my waist and love handle area that i was able to get rid of with ketosis in just 2 weeks (approx 7 pounds, strength was IMPROVED following ketosis).
here's some answers to your questions.
1. The type of ketogenic diet they use for epileptics is not recommended. That protocol calls for something like 92% of your calories to come from fats with 7% from protein, and <1% from carbs. Something like 80% fat cals and 20% protein is best for someone trying to spare muscle and burn fat.
2. Eating as much protein is not a good idea but you can eat as much meat as you want (red meat, bacon, fish, eggs, chicken anything that doesnt have carbs really (i.e, beef jerky). Like i said around 20% protein is good if you are trying to keep muscle and train while on the diet.
3. Cheese, now cheese supposedly doesn't have any carbs, but it actually does have a very small amount of lactose i believe. And for some reason it always reduces my level of ketosis when i eat it. Not to mention the fact that if you are prone, cheese will constipate you like nothing in this world. That being said I often crave cheese and do not limit my intake of it during ketosis.
4. I didn't end up needing any fiber for my first round of ketosis, but yes fiber pills do exist in chewable and pill form (metamucil makes one) and these are recommended as the drink mixes (i.e. citrucel, metamucil) have artificial sweetener, maltodextrin, and citric acid and will generally make you feel like shit during keto.
5. Artificial sweeteners, citric acid, etc. I wouldn't worry too much about them "slowing down" ketosis, they will temporarily reduce the amount of ketosis but it's not significant enough to affect your goals over a period of a couple weeks or more. You will avoid these things however, because aspartame can trigger the insulin response, and without any sugar being added to your bloodstream you will instantly feel the effects (no energy, mental fog). I only drink tea and water while in keto, once i had a diet cherry vanilla dr. pepper, never again. Also if you are trying to transition into ketosis, drinking diet drinks will only make everything much harder for you.
Cardio will be more difficult in ketosis, i recommend doing it for about 30 mins or so but reduce your resistance or speed (i.e. if you run on the treadmill at 6 mph reduce it to 5 or 4) because you won't have the same intensity, you can actually do lower intensity cardio for a longer period of time on keto however. Honestly I didn't even need to do cardio as much in keto, i only did it maybe 2x a week and had great results.
I recommend that you get Ketostix or an off-brand of ketone urinalysis strips, they will let you know if your diet is appropriate and what level of ketosis you are in, don't let the level bother you too much as it switches depending on whether or not you just ate a high fat meal etc. but use it to check periodically to make sure you are in ketosis. After you get used to the diet you can really tell whether your are in keto just by feel generally, but at first the strips help, but they are not 100 percent necessary.
Also if you are going to do it for more than 2 weeks, consider a targeted ketogenic diet (TKD) , or a cyclical ketogenic diet (CKD), both allow carbs at selected times to maintain workout intensity (somewhat) and your sanity. Search for them in the diet section on these boards you will find tons of info.
Hope this helps.