You'll likely do better first trying a recipe, and see how it comes out and we can tell you how to adjust it for your preferences, but a few things to consider when making meatloaf:
Don't squish the meat or work it too much while you're mixing it; you'll end up with a rather dense meatloaf. (unless of course you like that sort of thing).
Some people prefer on fattier grinds of meat for a 'juicier' meatloaf ... I personally go with 85/15 or fattier.
Mixing types of fat with different melting characteristics will also change the texture; for this reason, some recipes call for adding pork sausage, or a blend of ground pork, beef and veal.
Vessel is important -- some people will cook their meatloaf in a loaf pan; personally, I like a little crust on mine, but because of the grease that comes off during baking, I use a broiler pan.
Shape will affect the crust and cooking time -- a larger cross-section will need a longer cooking time, but the top may crust up too much; you can either tent with foil while cooking, coat with a glaze, top with bacon strips, etc.
Mixing the meat while chilled will keep the meatloaf less dense, but allowing it to warm up before cooking will allow it to cook more evenly. (so the outside isn't overcooked while the middle's still cold; especially important if you're not going with a glaze or similar)
Almost any vegetables can be added as a filler, if you pre-cook them to soften and remove most of their moisture so they're not overly wet. Onions, bell pepper, carrots, cellery, dark greens (spinach, chard, etc), summer squash (eg. zucchini, yellow squash) all work well.
To speed up cooking time, or if you're living alone and know you won't eat the whole thing, consider making smaller loaves. You can even make it in a burger patty size & shape for individual servings.
The meringue should be glossy and form soft peaks. When you take your whisk out of the meringue it should look like this:
The French say that when you take the whisk out of the meringue, it has to look a bit like a bird's beak, hence the way the meringue forms a soft peak slightly pointing downwards.
But to be honest, I don't believe that is you problem. I guess you just undermix your batter. People often say it has to fall like a ribbon or like magma, but I always thought that is hard to imagine. You can take a knife and cut through the batter. If it flows back immediately, it's ready. But let me tell you: One or two strokes too much with the spatula and the batter becomes unusable.
And one tip I can give you: The process of transferring the batter into the piping bag also 'mixes' the batter, so maybe don't go too far if you are unsure.
And as already said, it is important to tap the the tray from the bottom after piping as it helps to remove any air bubbles in there. Also, always pipe straight from the top (90° angle). This also helps the batter to smooth out.
I wouldn't recommend you to chance the amount of powdered sugar, as the French use Tant pour Tant (TPT) for their macarons, which means fine almond meal and powdered sugar are mixed proportional to each other.
When mixed perfect, it looks like this:
http://1.bp.blogspot.com/_WhPHUKwckUw/S4WP1eBE7pI/AAAAAAAAB00/gYqFjGOvEiU/s1600-h/5.jpg
When gone too far, it looks like this:
http://3.bp.blogspot.com/_WhPHUKwckUw/S4WP-q8RrdI/AAAAAAAAB08/7R6uO1uGfBQ/s1600-h/6.jpg
Maybe try counting your strokes while mixing, some people say that it helped them.
Best Answer
Frost it.
Most surfaces will be rough when looked at closely enough. Bubbles are introduced when you mix the ingredients together (perhaps more if you use a high-speed machine beater & less if you do it by hand) and as a natural part of baking, from baking soda etc. That's what makes the cakes more light and airy as opposed to thick.