Yeah that seems like a nice load to buy, and it's within your budget (although shipping will be just over £10 for all of it).
The gun's pretty good, my mate has a CM16. They're plastic and quite light, but durable and have a good finish. It's a good starter gun, will perform the same as the one from Action Hobbies you posted earlier, the only reason it's cheaper is the externals - RIS is more expensive than standard handguards.
The battery and charger seem like a good option, 1600mAh should last you all day, I've never flattened a 1100mAh (but I nearly always use semi).
I have some of those masks, they're good for the job and price. And the bottom half is easily removable if you want to.
Be careful with it though, some of mine are dodgy, the mesh is starting to come out, but a bit of super glue fixes it. Although mine were about £5, rather than £10.