Ok, so I don't know anything about low carb, I've never tried that one before. So I'm sure someone else would be able to answer that part of the question better.
For recipes, depending on the recipe, I have a few tactics. For recipes online that I just want to copy and paste and see if there is even a remote possibility that they would fit into my count for the day, I put them into this website for a general idea:
http://caloriecount.about.com/cc/recipe_analysis.php.
If I'm going to make a family favorite, or switch up ingredients from a written recipe (like changing sour cream for non fat sour cream), I calculate calorie counts for each item, add them up and divide by servings.
I keep a little book for my calorie counting, and in the back I write in recipes and their calorie counts (but I'm kind of a recipe goon, maybe that's not something other people do
) as well as counts I've already looked up for favorites at restaurants and my regular items (like a list of under 200 cal snacks that I can have).
Serving sizes... depends... for a casserole, I divide it up by 4 or 6 or whatever - whatever makes a serving fit into my calorie count. If that is 2 bites, it's not a serving size worth my time. For soups and stews, I measure out how many cups it makes and divide by that.
It was a little hard at the beginning, just because I didn't know how many calories were in anything. I know lots of people on this site use online programs that work for them, and I'm sure they will chime in with what those sites are. But it definitely gets easier as you get used to it - I could probably keep a running tally in my head by now if I wasn't worried about forgetting about all my 'just a bites'.
Good luck!! I look forward to hearing everyone elses great advice on this one.