Google that RS gold material if you would like more detail. For your amulet, the fury (again, dropping in price like bandos) is still generally considered the best choice. For your cape, you have got the trimmed skillcape, or the flame cape, or the uber-fire cape that you get out of giving up a fire cape and performing a minigame that's harder than combat caves. It's tough. Really tough. You have to do that quest for the ring I mentioned previously. It will not look perfect, however from what I have heard it's great stats.

Asking for the ability that makes the most money is quite vague, so you're most likely to get (and have gotten) some realistic replies. I will give a run-down of a few abilities you might be interested in (in the manners in which they're trained by most, therefore it is the most realistic - except for Hunter - jadinkos do not make money afaik but they're quite fast.

I gave reddish chinchompas as the profit making alternative. Grenwalls are another choice and more likely to earn money but they are a lot more immersion intensive and a lot slower exp/h - like runite's relation with Mining). Fishing from 90-99 would make about 46M about Rocktails (I didn't include the price of living minerals, but I am making an assumption that will be negated by any profits made getting to 90 Fishing), taking approximately 180-190 hours (again excluding levels prior to 90, and assuming ~42k exp/h).

Mining from 80-99 would make about 60M on gold ore in the Living Rock Caverns and take ~220 hours (supposing 50k exp/h). Hunter out of 80-99 would make about 35M on reddish chinchompas and take ~150 hours (supposing 75k exp/h). Ideally the best way would be to receive 85 Dungeoneering and only do frost dragons if you want money, but you won't be considering cheap OSRS gold getting any 99s fast.