if your case is broken as you state, it seems obvious that there is damage even on the inside. The dropping is most likely not covered by warranty - but if you are not comfortable working on the phone I would not recommend it you try. With these things I feel, only do it if you are prepard to loose (the function of) it. So, if you are adventurous and have a plan B - go for it, its fun.

it is hard to quantify 'expensive' - when your business relies on it. If not having your computer and data put's you out of business you may have to have it repaired - but if buying a similar machine and putting your data on it gets you over the line, that's fine too. Maybe you should let a good professional handle this - I have seen to often that business owner panic at a computer breakdown, because they see their business being threatened - and it is hard to stay calm and objective when troubleshooting if your financial existence is at stake

that is bad - but at least you can see it when there is light. It looks that there really no parts available (from iFixit) to help you with your repair. Short of finding a broken wire or cold solderjoint there does not seem to be much you can do.

As long as it is not used as a mounting point for something else, I guess there is no problem removing the drive. Why don't you try to disconnect it first (power and data) and see if the machine boots and performs still ok?