Man, you're already going to high school reunions (I'm 24)?! I don't think I'll bother until the 10 yr, and even then, I'm on the fence about it. Nobody I'd really care to see.
What kind of veggies do you know that you like? If you're not sure about their status (as a legume or grain), no worries, we can set you straight on that Most veggies that are not legumes or starches (or fruits haha) are fairly low carb and you really don't have to worry about how much of them you eat! Broccoli and asparagus are my favorite.
Starting off, I would say focus on a reasonable serving size of meat/protein (if you're looking to lose fat now, calculate your lean body mass and eat about 1g of meat per lb of lean body mass, that's how much you should have in a day) for the meal, and then have plenty of veggies. Eat them together, eat one at a time, whatever, stop when you're full or the plate is empty. If you're really worried about portions, you could use a tracking site like FitDay and enter in rough serving sizes to determine how much you are eating, but honestly, starting off, I think it's most important to just EAT and if your hunger signals are off (for example, you eat like 2 lbs of meat and some veggies and are still hungry), they will adjust over time as your body gets more comfortable with itself.