People have been giving some really good advice. I'll add my thoughts for consideration.

Given your stated goal of having something nice enough to go out to dinner, and assuming a tight budget, here is what I would recommend.

I'll also assume, for pricing purposes, that you are purchasing from the Scottish Tartans Museum. As you are planning on ordering the kilt from us, it makes sense, but keep in mind you may find other suitable items elsewhere are various prices.

FOR THE TIGHT BUDGET:
In addition to the kilt, you'll need:
1) a pair of our standard kilt hose. $27.95
2) a pair of garters, either elastic or self-tie. $24
3) a functional day-wear sporran. Our economic models that start at around $60 are nice, but you'll probably want to purchase a better belt than what comes with them, which will run you another $25-$30. Or you can splurge a bit and get one of the nicer day-wear that will run you in the mid-$100s. These will be supplied with a nice belt.

As you plan on having something that can be dressed up a bit to take your wife out to dinner, I'd advise you get a black leather sporran, and if you don't already have a tie that would look nice with your kilt, buy a solid color one, which we sell for $24.95.

As for shoes, you likely have something in your wardrobe that will work. Same thing with the shirt. Unless you plan on taking to wife to a place that requires jacket, you can wait a while on the Argyle jacket. You can always dress the outfit up with a sweater.

IF YOU HAVE A BIT MORE OF A BUDGET:
1) You might want to consider upgrading to the Lewis hose, which are a nicer quality and will give you a wider range of color. $48
2) Definitely get a nice mid-range sporran rather than an economy model.
3) Consider adding a kilt pin, $20 to $25 in most cases.
4) Consider adding a sgian dubh, which come in a very wide range of prices.

Lastly, I would say that eventually you'll probably want a nice Argyle jacket. But this can be something you budget and save for, like the kilt. Unless you know up front that you will be attending a lot of functions that would require a jacket, there is no urgent need, and this is a high price item. So wait till you can save some pennies, and have recovered from the cost of the kilt a bit. :-)