There's no such thing as a sleeper service in first, you can eat when you want and drink when you want. If you want to sleep straight away they will facilitate that by making up your bed as soon as possible after take off.

Where I had an overnight flight in F, I ate in the pre-flight dining area of the lounge with the intention of not eating on board. However, when I seen the menu there was a starter that looked nice so decided to have that with a glass of champage before going to bed.

Some crew will ask early on how do you want to spend your journey so they can tailor the service to your needs, others will just work out what your preferences are as you go on.