Most of the alterations were definitely necessary, however it turns out adding to the side seams was a mistake - the finished dress turned out a bit big and overall a bit frumpy. It was worn a couple of times and then shoved to the back of my wardrobe and not worn again... until me-made March prompted me to re-assess my me-made items.
I couldn't really take it in at the side seams, as that would have made the pockets too narrow and unusable, so I wasn't really sure how to make the dress more fitted.... so I didn't. Instead I hacked about 4 inches off the bottom of the skirt and re-hemmed it.
The skirt is still as un-fitted as it was before, but the shorter length has given it a bit of a 60s vibe, and it is finally wearable. More than that, it's super comfy! So comfy that I wore it two days in a row after modifying it.
An interesting thing that I want to mention, incase anyone else can learn from my mistake, is the placement of the pockets. When working out the pattern I didn't quite thing through the height the pockets should be - I forgot the seamline for the pocket was the top of the pocket, not the bottom. So the pockets on this dress are a little low... I can only just reach the bottom of the pockets with the tips of my fingers. But that's definitely a mistake I won't be making again!