Some phrases are downright very standard, some others are really recent “teenager slang”:

• savoir sur le bout des doigts (to have down pat): correct but more commonly used as connaître sur le bout des doigts

• ça fait envie (it’s tempting): correct, quite common

• ça craint un max (it’s dodgy/risky): very colloquial, sounds like “bad boy” slang. It can also mean “disappointing, upsetting” (ex: J’ai raté mon examen, ça craint)

• à moitié (sorta, kinda): correct , and is very common. It is rather negative, ie “not so much” (ex: j’étais à moitié content de mon travail means you were not really satisfied)

• ça fait deux (we don’t see eye to eye, we don’t go together): correct, quite common in familiar uses, but is always used along with mentioning 2 persons, or more commonly one person and one field of knowledge or expertise (ex: Moi et les maths, ça fait deux)

• je suis chaud (i’m down, i’m up for it, i want to): very common nowadays among teenagers, would sound a bit weird in the mouth of anyone above eg 30

• c’est chaud (it’s complicated). same comment as je suis chaud. Depending on the context, it can also mean that’s a risky situation (ex: c’est chaud pendant les manifs des gilets jaunes, il vaut mieux rester à l’écart)

• c’est ceinture: the more common phrase is faire ceinture, that means to go without something (ex: on doit faire des économies, on va faire ceinture et ne pas partir en vacances). If used in a certain context, it can be obvious you are talking about sex, it is then used as an innuendo to mean no sex (ex: je n’ai fait que travailler pour mes examens, je n’ai pas vu ma copine, ça a été ceinture pendant un mois !)

• nous y voilà: can mean plenty of things depending on the context, ie here we are when arriving somewhere or that’s what I was waiting for if you want to express some relief after waiting for something