To remain in ketosis you need less than 25grams per day I think. These will all be made up of incidental carb's from whey, veggies etc. This number is obviously slightly arbitrary as we are all different sizes, metabolisms, etc but I would NOT eat any carb' sources early on in a paleo or keto diet as they will make you feel RANK afterwards. After a couple of weeks of this a good carb' up will make you feel amazing and can become a regular feature.
The biggest problem I had when on a no carb' diet was everyone else's opinions about it. If you can cope with this, you'll be golden.
Don't call it a comeback