Since sending off my work, I've had more time to think. About what has made it easier to complete this course, and what has made it difficult.
Good brushes. It's important to find brushes that suit your way of painting and which have the right spring and water holding capacity, with a really fine point. I found that for me, my Da Vinci brushes with long fine points were the biz.
Good paper. One of the most difficult aspects of the course for me was the variability of the paper provided. I was used to the paper, as I bought some to practise with before starting the course and was very happy with it. But the pad I was sent was a disappointment. I bought a replacement one which was much better, but not perfect. I am going to try contacting the manufacturer to find out why it is so variable. It's almost impossible to do delicate watercolour work on paper that has patches which behave like blotting paper!
Good Paint. Top quality artist's watercolours are essential to being able to render realistic images and cannot be skimped on. But it's important not to get seduced by the often romantic blurb of the manufacturers. I made a point of trying watercolours from all the major manufacturers and all of them are excellent. Some brands have more colour choice. One brand has a bewildering selection amounting to hundreds of different colours. Those new to watercolour often think more colours are better, but when learning about mixing and about the different properties of paints it's better to stick to a limited selection. In this respect, some companies are very helpful and put together sets which are useful for beginners and reasonably priced when compared with buying the tubes or pans separately. However, it's best to be aware of which colours you are likely to need, as some manufacturers have a tendency to produce sets with colours chosen for Landscape artists. Manufacturers also give different names to colours, but a quick look at the pigment number will tell you whether they are likely to be the same, eg. PY153 (Pigment Yellow 153) is named Indian Yellow by some manufacturers and New Gamboge by others, but essentially they are the same colour - a wonderful warm, transparent, egg yolk yellow in mass tone and a cooler yellow when used in a light wash.
The important thing is to get to know your colours really well, know what pigments they contain as well as their names, play with them, mix them, make notes and keep those colour swatches and mixes safe, you never know when you'll need a particular shade for a painting, and having it to hand makes life much simpler.