I am probably going to sound like a salesman for Artix Entertainment here (even though I'm not, they don't pay me a dime to endorse them, I have paid them thousands to support their games because I deemed it worth it) because they do make it worth it to support the game. I am going to tell you exactly what is worth buying so you can minimize what you spend if you are financially challenged or if you are frugal, if you wish to spend more, that's up to you.
Get a membership! Go ahead (if you can afford it) and buy a year's membership, and add the 5,000 AC's for $5. I cannot stress that enough! It is well worth it! And with your bonus package, get the Infinity Titan pack. I recommend getting this during a 50% bonus sale, especially if you're buying a year, it will net you approximately 18,000 AC's!
IF YOU CAN AFFORD IT, get a 40,000 AC package DURING A 50% BONUS SALE to net you 60,000 AC's and an IoDA. This will assist you in purchasing Nulgath pets and bag / inventory space and bank space.
Grab a Cape of Awe from Binky in Doom Vault.
If you don't use your IoDAs (you actually get two, a Mythical and a Bonus) on a Necrotic Sword of Doom (which I personally wouldn't, I'd use it for an Oblivion Blade of Nulgath (rare) and a Nulgath Challenge Pet, but that's me), you could level to level 61, hope you can get carried in Ultra Ezrajal, Ultra Warden, and Ultra Engineer 28 times each, and get your Exalted Apotheosis. I personally wouldn't do that right at level 61 though, that might be considered rude, and after all, Dr. Hannibal Lecter would wish for us to be courteous now would he?
Nay, what I personally did was grind Necrotic Sword of Doom....after I got Sepulchure's Doom Knight Armor. It was daunting, but it was worth it in the end. Part of the challenge of the game is leveling your weapon up, and receiving end-game gear at the beginning would not exactly be right, would it? Let me reiterate to make this absolutely clear if you plan to get an NSoD, or this will be absolute HELL for you, a literal nightmare....
#1. Buy a membership, minimum three months, as this will take you 6 weeks to 2 months to grind comfortably....
#2. Grind Sepulchure's Doom Knight Armor. This may sound like an extra step, but it will save you time, trust me, as it unlocks certain quests.
#3. Grind the SDKA quest Commanding Shadow Essences in Shadowfall until you get your NSoD. :)
There is plenty of shit to do in the game, it's not just grinding, unless you wish to just do that. Personally, I say go ahead and advance your character to 100 doing quests and obtaining your Necrotic Sword of Doom.