My advice, if you're not confident, is to stick with a simple design. Use beautiful paper, but keep the design simple to minimise the 'fiddlyness'. You'd also need access to a printer, and some weekends to put the invites together.
Something like this, is reasonably easy to make. The paper is Cristina Re paper, which you can find in most invitation paper shops.
Or a few layers of paper, DL-sized invite like this one.
As for paper, shop around a little. Officeworks is a good start, but check out some art stores too.
As for when to send them, it depends. I would say give yourself at least 3-4 weeks before the wedding to get all the invitations back (so that you can finalise numbers), then allow perhaps people 3-4 weeks to respond. So, I would say send it somewhere between 6-8 weeks before your wedding.
If you have a B-list of guests (whom you will only invite if there are declines from the first round of invites) OR if people will have to travel/organise accomodation for your wedding, then it's probably best to send it out earlier.
Good luck with it