Scottish Person here!

As a guide the entry in the wiki is pretty spot on.

For your scenario Id say definitely rent one first unless you are SO set on having your own. If you are in Scotland there is no shortage of kilt hire shops and its fairly simple. They take your measurements, give you a decent fit on everything and give you all the accessories to go with it, and you can try it all on as a complete outfit in the shop, easy as and not too expensive. Only downside is that kilt shops usually only have a select number of tartans for rent so you'll either need to pick the closest looking one or just go with one you like.

As for the style you should ask the others what they are going to wear. Typically it is the Bonnie Prince Charlie version for weddings but there are loads of different ways to style kilts and people now seem to be going for a more simple look such as a Crail/Argyll jacket. Then each wedding party has its own colour scheme for ties and socks, and overall style so really best to just see what the others are wearing and rent that.

If you really want to get your own then Id also say get it in Scotland. I mean... its Scottish, who else is going to make it better. And throw some business our way. But also you will probably have more access to the different tartans from the mills and have a greater choice of styles and accessories. Downside there is the fittings but as long as you get the first one and the jacket sorted while you are there you shouldn't have too much trouble. The kilt itself is very adjustable as someone said already so its the jacket thats the issue. Hope you get it sorted and enjoy looking awesome!