I do not believe you want to RuneScape

I am not an expert on helms, but RS gold if you're slaying you want the full slayer helm because of its bonuses (likewise Salve amulet if it is applicable ) and Verac's helm otherwise. For boots, you'll probably need to stick to dragon. You will find better boots, known as"ragefire" I think, but I do not believe you want to devote your bank on them. For gloves, possibly barrows gloves out of RFD or possibly goliath gloves in the dominion tower. Goliaths require you to have done plenty of quests and lots of arcade-style combat in a big tower full of pursuit bosses. Something you might pick up when you have caught up on your questing generally, I think.

For the ring, there's a very pleasant free ring you get out of"A return to stone" (I think that is what the quest is called). It starts in TzHaar city, in the birthing pool. It is all of the fremmenik attack ring bonuses, and a bunch of rather nice reusable teleports, along with a battle bonus against the tzhaar. Or you might get the Berserker ring, that delivers a strength bonus, or you might get the explorer's ring, which offers a few free alchemy spells every day, or you could get an Onyx ring and imbue it in mobilising armies.

Google that material if you want more detail. For the amulet, the fury (again, dropping in cost like bandos) remains generally considered the best bet. For the cape, you've got the trimmed skillcape, or the fire cape, or even the uber-fire cape that you get from giving a fire up cape and doing a minigame that's harder than combat caves. It's tough. Really tough. You have to do that quest for the ring I said previously. It doesn't look great, however from what I have heard it has great stats.

Asking for your skill which makes the most cash is extremely vague, so you're likely to get (and have gotten) some unrealistic answers. I'll provide a run of a few skills you may be interested in (in the ways in which they're educated by most, therefore it is the most sensible - except for Hunter - jadinkos don't make cash afaik but they're quite fast.

I gave red chinchompas as the benefit making option. Grenwalls are another choice and more likely to earn money but they're a lot more immersion intensive and a lot slower exp/h - similar to runite's relation with Mining). Fishing from 90-99 would make about 46M about Rocktails (I did not include the price of dwelling minerals, but I am making an assumption that will be negated by any gains made getting to 90 Fishing), carrying about 180-190 hours (again excluding levels before 90, and buy RuneScape gold assuming ~42k exp/h).