If you find you enjoy your dressmaking class, and plan to make more dresses in future, consider buying a dressmaker's dummy and adjusting it to your exact measurements. It will make fitting dresses so much easier.
Search the internet for sales/remnants/offers at specialist fine-fabric shops. To avoid cling and make most fabrics hang well, you'll probably need to make a lining, as well. White or cream fabrics usually need lining, otherwise they can be transparent.
If you are wanting a vintage style, there are also online sellers specialising in real or reproduction vintage dressmaking patterns.
Set aside a space to leave sewing things/ironing board standing ready for action (pressing as you go is usually gives best results, although that naturally depends on the fabric). It can be a real bore to have to get out/pack away all your sewing things every time you have a spare hour or so to do a bit of sewing. And doing dressmaking well usually takes time.
Strongly agree with advice by earlier posters to try making some other small items first, and, when it comes to the dress itself, do a dry run with cheap fabric - even old sheets, which you can purchase v cheaply at charity shops, will do for that.
Especially if using silk or velvet, avoid a design needing buttonholes. They are really hard to do well without lots of practice. You may find that you have a gift for them, however. Good luck! When it works, it's magical to turn a piece of flat fabric into something flattering and three-dimensional.