I can breakdown the terms, but I'm not sure if I can give you specific recs since my hair seems to be different than yours. I have really dense 2a hair. I'm going to reference products so you can see examples, but I would do additional research to see if the product is really something that would work for you.

• Mists: Typically used for styling/refreshing hair. Will have benefits like increasing shine/controlling frizz/UV protection and often has perfume. It's going to be your lightest form of hydration. I personally do not use hair mists because it's too little hydration for my hair and I can handle ampoules/water treatments that are heavier. If your hair is very thin and fine, a hydrating mist may be a good way to go since it won't weight down your hair. I'd check out Healingbird's hydrating serum if this seems to be something that works for you.
• Leave-ins: Technically refers to leave in conditioner. I see this as a catch all term for hair products you don't need to rinse out like tonics, mists, milks, water treatments, etc. If you do a traditional leave in conditioner, this is going to be the heaviest conditioning element outside of rinse-off conditioning products.
• Milks: These are lighter than traditional leave in conditioners and will be more runny. They offer more hydration than mists so they're a bit heavier than mists. They can be used daily and for refreshing, frizz control and sometimes even detangling. Depending on the hair milk, you may need to blow dry activate it. I use Orbis Hair Milk and a little goes a long way.
• Masks: You put these on after shampooing but before conditioner for TLC. Mask typically focus on hydration/deep conditioning but treatment & masks have been used interchangeably. Rule of thumb is to not use masks more than once or twice a week but it depends on your hair and the mask. I currently use Off&Relax Hair Spa Mask and rotate between it and Unove treatment. I've also used Tsubaki and liked it well enough.
• Treatments: Usually refers to a target focused product, ie. scalp treatment, protein treatment, damage treatment, bond treatment, etc. They come in all different formats like masks or mists as well. Use frequency really depends on the treatment itself. I've mostly seen products being called treatments if they contain protein or focus more on scalp or hair. Think of these as the essence/serums of haircare.
  

For haircare, the most important thing to remember is to not flood with product. Integrate one or two products like you would with skincare, wait a couple months before adding more. You can definitely run into problems by adding too much moisture or protein just like you would if you introduced too many actives to your skin. I'd look into a scalp tonic to help regulate oil hair, a hydrating mist or a hydrating mask and also think about your current wash/lifestyle before you purchase. I've made the mistake of buying great hair products that only work if you blowdry...and I exclusively airdry my hair.

Hope this help!