The recommendation to train Slayer comes from high level players looking back and saying,"meh, wish I coached Slayer, now I'm 138 and also have 10 levels to go...". The skill does offer two main benefits and that is: You constantly kill something distinct. You are able to cancel a task if you don't like killing something. The disadvantages is that eventually you get tired of it as well, and you may just block 5 monsters. Additionally, some critters aren't good for coaching melee. I would urge training through Slayer, anyway, but you have read the facts, so your choice.
In terms of recommended equipment, a Black Mask or even a Slayer helm is an absolute must. Beside that, you only require a whip (or even a twisted weapon out of Dungeoneerin). The rest is left up to you. For starters, I'd get Torag's plate and legs, which supply the best protection-value ratio in the game (s'much as I know), black dragonhide for the magic-based missions, and begin working on the Recipe for Disaster quest, which delivers the best stat-boosting gloves in the game. I'd also get a ring of riches (can not hurt), an amulet of glory and dragon boots - the latter if you have spare change, it is just a tiny Strength bonus. In general, the whole thing should cost you 2.5-3m.
Combine both and powerslay! It follows that you simply use your best att/str boosting prayers and super baskets in