Main quests you'll need are,
Horror from the deep (book is useless, even for range tanks because of the low cost, range bonus and the prayer bonus)
Lunar Diplomacy (Vengeance)
Recipe for disaster (I doubt you want to get swift gloves and mercenary gloves would be a pain to replace each time you die, I'd recommend you get these)
Animal Magnetism (Accumulator is a must)
Desert treasure (I'd recommend this if you ever want to brid on this account)
Forgiveness of the Chaos Dwarf (Hand Cannon)
Also, unless you will be wearing ganodermic on your range tank, I don't really see the point of getting 85 defence. I'd recommend staying at 70 for armadyl (Only go for 75-80 if you can afford spirit shields and nex armor)
Other things you might want...
- Mercenary gloves (Better range attack than barrows gloves if you ever decide you want to PvM on this account)
- I'm making a similar account to you, except my range and mage will both be 99 so I can switch between a chaotic crossbow and a polypore staff for pking to keep things interesting. I suggest you do the same since only using a chaotic crossbow would get pretty boring.
- If you do decide to make this account a range/mage tank, I would highly suggest you get augury on top of rigour. A little extra effort, but it's definitely worth it.
- Armadyl Storm Spell (Absolutely great for PvM + PvP, definitely worth the grind)
- Imbued Rings (If you have the time, head on over to Mobilising Armies and invest ~25 hours into getting imbued rings. It is AFK able so it's not to bad.)
- Summoning (Definitely worth training as there are so many useful things for PvP + PvM, yak, unicorn, titans, ect...)
That's all I could think of off the top of my head, goodluck with this great account ^_^