Hi,
I would say no to the mandarin. I tried keeping a scooter blenny (also a dragonet with the same issues as a mandarin) in a 120l well established reef tank. Even though it ate frozen it didnt do well and lost a lot of weight in a short period of time before I gave him to someone with a much larger tank.
It is possible to culture pods for them but it is a full time job and one that you have to be 100% committed to. to anyone thinking of going down this route I would say culture the pods and feed them to your tank for at least 3 months before you have a fish that is reliant on you constantly culturing food for it. If you can keep it up for 3 months with no "reward" then you will probably be able to keep it going once you have a mandarin.
Hawkfish - as mentioned these are known for eating ornamental inverts (mainly shrimp) but I also know people that have got away with it.
firefish - I'm not sure you could keep two or not. I had always read that unless you have a large tank or mated pair then only keep one but I have had people argue that with me before.
I dont know anything about jawfish but the perc and crab will be ok.
8 fish in a 100l is pushing it a bit too. it is doable but you will need to have a top notch skimmer on there and do plenty of regular water changes as well as having enough liverock and water circulation for the basic filtration.