A couple of random thoughts--

1) always get a kilt that fits now. You may, or may not, take off (or add) inches around the tummy.

2) Irish National tartan is a good choice-- as is any other non-clan-specific tartan, unless you feel an attachment to a specific clan tartan.

3) If you are looking for a "neutral" kind of shirt to wear with your kilt, a white or light blue button down oxford cloth shirt (short or long sleeve) is probably your best choice. Try WalMart for around ten bucks.

4) As far as accessories go, you've nailed it. Belt and sporran, and a kilt pin if you feel like it.

5) Hose-- any colour as long as they are darker colours-- white is for bands and rented kilts worn to weddings, so avoid 'em. Stick with flashes that are the same colour as the narrowest stripe in the kilt-- tartan flashes are just so much tartan over-kill.

6) and one other thing-- if you are in the presence of children or ladies, underwear should be worn.