Fiber is a carb. You can't eat it without consuming carbs. But, you can subtract fiber from your carbs. So, it doesn't count. If you eat 10g of pure fiber, you can consider it as 0g of net carbs.

The calorie level is probably because MFP is notorious for giving really low calorie goals. If the keto-calculator tells you that you'll have success at that level, start there. Don't worry about MFP.

You can change your mfp goals go to my home, goals, change goals green button at bottom of page, select custom then continue, change the settings for carb, fat, protein % and any others you want to change, then click on change goals green button at bottom of screen. Your food diary goals will then be closer to ketogenic goals but not necessarily perfect, can play around with it to get close as you can but mostly i just keep a note of what my goals are and do not pay too much attention to mfp targets accept to use mfp as a monitoring system to reach my personal keto and calorie targets not mfp targets..

The keto calculator recomends very small calorie deficit for very gradual weight loss. Personally I imputed a goal closer to mfp recommendation for my selection of 2lb per week loss. I usually lose 1 or 2lb a week. For first several weeks just for a rough guide i set my mfp settings to total carbs set at 5%, protien 20% and fat 75% on mfp. % does not really matter so much though as is very relative to the total amount of calories. I concentrated on keeping my net carbs (Carbohydrate total minus fiber total = net carbs) under 20g per day often way under just first few weeks. I aimed to get the amount of protein recommended by keto calculator and i made up the rest of my calories with healthy fats.

Now 10 weeks in and reasonably confident that i am ketogenic adapted. As a rough guide I have set my mfp goals as 15% carbs, 25% protein and 60% fat. I now aim to keep my net carbs under 35g max, my protein still the amount recommended for me on keto calculator and still make up rest of calories from healthy fats.

I would say do not pay too much attention to mfp total numbers. Just start by getting your net carbs down to 20 or under, meet your protein needs and then hit whatever your calorie goal is by filling in the rest with healthy fats. some people do not even worry about calorie goals first few weeks, just get used to new way of eating and then bring in paying attention to calorie goal.