Ranged - Crystal bow is not too bad, but it RS gold is not the ideal weapon for somebody with your stats and cash. You ought to at the very least make a Royal Crossbow. I don't understand how to do so since I don't have one, but I'm told it's simple (and also the Royal Xbow is a grade 80 weapon). If you are like me and cba to earn the crossbow you can always buy a Zaryte (60Mish), it's a grade 80 weapon, demands no ammo like the Crystal bow and also degrades very slowly. The tier 90 weapons are the Ascension crossbows, both worth 255Mish every so to buy the two you'd have to spend 500M+.
Nex armours are good also, but they're definitely overkill for Slayer. I have Pernix and I do PvP and bossing using it just. I'm really using it to camp ascension dungeon atm, but that's because I'm attempting to get 99 Ranged this weekend and need to have as much exp per hour as possible.
So that you've already got quite a bit of info from Aza, Fatia and Kamil, I'd just add a couple of things: A player with maxed stats like you ought to be looking to have the POP (Player owned ports, a brand new D D) armours. These come in 2 types- a superior, non tradeable version, or a slightly weaker, tradeable edition. However, these armour sets require a SIGNIFICANT quantity of time to obtain. Till then, I'd suggest utilize the Bandos and Armadyl you've kept in the bank. There is not much to profit from purchasing Nex sets when you will be selling them directly after you purchase POP equipment.
Please be aware that all weapons and armour are now organized TIER shrewd, by level. Dragon requires 60, and thus is Tier 60; Likewise Barrows is Tier 70. All weapons of the exact same Tier have the exact same DPS- a rune scimitar is equal to some rune warhammer now. Similarly, all armour collections of the same tier have the same lifepoint bonus- Bandos armour provides the identical LP increase that Armadyl, or the Robes of Subjugation give.
Currently, the maximum tier is cheap OSRS gold level 90. You shouldn't hesitate in the slightest, and go ahead and purchase drygore maces. The Drygore mace in my view is the very best to get due to 2 reasons- the first being that it's marginally more affordable than the Rapier or even Longsword, the second being that it has a +9 prayer bonus.