Goodness what a lot of posts 
Thanks Jiminy for being around to provide all those answer as well 
@Naschkatze
B - Greek yoghurt, full fat with strawberries (BC light - breastfeeding.)
Perfect!
S - Boiled egg with salt and mayo.
Again, fine; hopefully once you're fat-adapted, you won't need to snack, but this kind of snack is perfect (and I'm assuming it was full fat mayo?)
L - Salad with a whole avocado, cucumber. Dressing made from mayo and lemon juice.
Sounds OK - an oil-based dressing might have been better, as it would have been carb free, and you would probably have ended up having more fat than this, which doesn't sound very much - although obviously I can't see the amount of dressing that you made!
D will be - Lemon chicken with spinach, mushrooms and broccoli.
Sounds lovely! But again, how are you cooking this, and how much fat are you using?
If I feel peckish I have some celery sticks to eat with cream cheese. Or maybe a spoon of peanut butter. Are these okay?
Cream cheese is better - peanut butter is quite carby, although this does depend on the brand; some are much carbier than others, so it's always worth checking the back of the pack
Questions: Is a whole avocado too much?!
Not really, when all you had with it was cucumber!
Am I allowed tea with a bit of milk?
Only if it's genuinely just a splash of milk - and if you're not having multiple cups of tea
How much butter for cooking or eating with veg? I don't want to over do it.
As much as you like! This is a high fat way of eating, so the more the better!