Plan snacks and things you like to eat and bring them from home. Find things that help with the nausea. For me, drinking soda water helped. Making sure I ate regularly did as well and I always pack lunches for work anyway, but I was extra careful. I also ate whatever I wanted that made me feel better, which generally was pretty healthy. It really isn't a time for stressing about diet.
I also found getting some fresh air and taking a walk in the middle of the day helped. I would plan it for when someone was eating something especially smelly for lunch.
Do you have the option to work from home at all? I work from home several days a week anyway, but I definitely made sure I took full advantage of it and worked from home when I could on the worst days (and I also took a nap!). When its really bad, take a sick day. That's what they're for and there's no reason to suffer.
As for when to tell, I would tell them when it affects your work or future plans and take into if/when you'd feel comfortable disclosing any bad news to them if you were to have a loss. I had a mc before this pregnancy, so I was in no hurry to talk to anyone about being pregnant. I have a lovely supervisor and colleagues, but I knew there was no way I'd want to share that news with them if it happened again (even when I took off 3 weeks for the mc, I still didn't tell them that's what it was). So I told my supervisor at 12 weeks when I was confident everything was going fine. I would have probably waited to tell her later, but I had an important meeting where we were discussing (one-on-one) my plans for the next year. Obviously seemed important to mention I wasn't planning to actually be around after February!