Welcome Aridane!

In answer to your first question:
Impact carbs is the carb count after fibre and/or sugar alcohols has been subtracted. For example, in the protein bar you mentioned, it probably contained malitol (or a similar sugar alcohol,) that 'supposedly' does not affect your blood sugar, thereby allowing you to continue burning fat. BEWARE - these sugar alcohols affect everyone differently - some people stall on their weight loss, others get bad diarrhea (sp?), etc. Another reason you might see the term 'impact carbs' is because fibre is deducted because fibre's gonna go right through you and also not affect your blood sugar. For example: a medium apple has approximately 21 grams of carbs and 4 grams fibre. 21 - 4 = 17 impact carbs. Does that make sense?

In response to your second question:
It's totally up to you! Check out the Nutrition and Supplement forum by clicking here Personally, I take a really good multivitamin (sans sugar, of course,) calcium + Vitamin D (to absorb the calcium), Vitamin C, L-Glutamine, Chromium, and Vitamin B12. I choose not to take an additional Iron supplement (there's some in the multi vite,) because I eat ALOT of meats that naturally have Iron in them.

Feel free to post with more questions. Happy LCing!