裝cam - Better if you install cam. If she really steal or mistreat the children then you have evidence to call police. Better be safe than sorry
比本簿仔佢mark下數 - Yes if you need her to do food shopping, but beware some 街市小販 make up larger $$$ on the receipt so the maids can cheat more money from employers. Better to make her only shop items from supermarket or make her go with you and carry for you. I usually make her come with me when I buy a lot of heavy things, then occasionally when I buy some small items from 街市 when I pass by (I am ftm)
洗頭沐浴露? - Depends if you want to pay for it. It's not necessary to include shampoo + soap but some employers do allow the maid to use the family's supply
手提電話+card? - Unless you need the maid to regular take children to school / playgroup, then not necessary at all. They all have their own mobile phone(s), just ask her for her number if you only call her occasionally. Most HK companies don't provide mobile phones for the workers but the bosses still have a right to contact you on your personal mobile phone right? If you think you need to provide her with one, better to give her a cheap cheap old phone with no smartphone feature with phone card with no SMS / no data
出街搭車比錢好定用八達通好?- Again, not necessary if you don't need the maid to travel regularly (take children to school / playgroup). If they lose your 八達通 you can't get the money back! Better to just give coins every time if you only need her to travel once in a while
最重要的我張書枱放在廳,我是否要裝d信件等收埋?- Yes yes yes, lock them up. Or if you have a room with all important documents / valuables, better to lock up this one room when you are not home. Tell maid to only clean that room when you are home
Better to get use to new habit right now than to regret if your maid steal your financial documents and do something bad. You can buy a separate document cabinet with lock if it helps. I also used to "手袋長期掛廳" but now "手袋長期掛主人室"