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Energizers and nutrients are used to encourage yeast health/activity to get a good start to fermentation or prevent extended/stalled fermentations. For some recipes, additives such as the fruit or spices used can add enough goodies that directly adding nutrients or energizers is not really necessary. Usually those are only really important when making traditional meads as the yeast need a few extra things other than just the honey to munch on.
Could you post the recipe you used? That will help us help you. ;D
Back to the nutrients and energizers - think about your own diet, or if you remember biology class, the way bodies fuel themselves is to break down glucose into energy, but you know yourself if you were to eat a diet of only sugar, you wouldn't last too long before you started showing signs of being deficient in proteins, fats, vitamins and other nutrients that keep the energy-producing stuff working efficiently. Same goes for yeast, and honey's pretty much straight sugar, not a whole lot else in there to promote healthy yeast. Glucose is great fuel but it's not great for cell-building, and that's what yeast is doing at the beginning - it's replicating, not processing.
And the added sugar? The one reason I can see for including it is that it's generally significantly cheaper than honey.
So for your second question, with your recipe, it won't throw off your final product, but it might take longer to get there. Show meads (just water, honey, and yeast) take a really long time because the yeast only have sugar and don't get those other nutrients they need. The lemon and vanilla you added are more for flavor and don't add the things the yeast need. If you can get your hands on some nutrients and energizers, I would suggest adding what the recipe called for. The good news is, you can add those things at any time near the start, before sugar breaks, and you will still be fine.