Gracey, I think your lai see amount sounds good to me. Helpers really appreciate the cash. We don't really do Christmas gifts so I won't be giving one to my helper but will give her a Christmas lai see - probably just a few hundreds though; we already gave her a bonus for completing one year with us this year and will give her a raise early next year. What's fair really depends on what you can afford. One thing I'd keep in mind is - I'd like to motivate my helper by giving her slightly bigger bonuses every year or a raise every couple of years she's with us. So I keep in mind that I'd like to keep raising the amount, when deciding the amount in the first year.
About eating with the family at parties, my helper sometimes eats with us, sometimes not. Actually, sometimes she eats before everyone because for our lunch gatherings we tend to eat really late and she gets hungry. If you're the host, there might also be work to be done and you might end up eating last/when everyone's done yourself so it's not necessarily discriminatory to the helper. My husband, helper and I never end up eating at the same time because one of us looks after my son while the others are eating. She might also prefer to eat in the kitchen where she can be comfortable and can take as much as she pleases which might not feel open to doing if she's at the table with you guys. Do what feels right and natural I guess.