Finding, deciding and purchasing the fabric's, trims and other bits and pieces I'd have to say has been one of the hardest things I've had to do. At time's i wanted to scream but instead thought this is what the real world is going to be like and I'm going to learn from these situations and problem solve.
1. Orders do get lost!!!!!! So make sure you always follow things up. 
2. Orders can take longer then promised. Be organized and try to place orders ASAP so you have more time up your sleeve if things don't go as planned.
3. Orders can come in the wrong colour, shape or size! If you need the product urgently you need to learn to compromise and find a medium that you and your suppler are happy :)  
4. Suppliers to run out of stock. So be Accurate and order the right amount the first time.

Overall I'm extremely happy with the fabrics, trims and other product's I've purchased and can't wait to see all the bits and pieces turn into a show stopping garment!