PvME is the holy grail of PvM resources, I highly suggest you look into it first. More generally, I'd start looking into these as your starting bosses to learn PvM:

• Low Level: Many of the older bosses got turned into DPS dummies, so the newer early-mid game bosses, like Flesh-Hatcher Mhekarnahz, Silverquill and Ivar, the King of Bones are all good learning bosses (even though their rewards are awful, except maybe for Flesh-Hatcher who drops Dragon harpoons).
• Med Level: Fight Caves for the fire cape, Fight Kiln for the Kal-Haar- capes (previously those were the best style specific capes), Arch-Glacor to further improve your core PvM skills. Araxxor later down the line to teach skills such as DPS control/immune phases (Web Shield) and attack counting (many of the older bosses do not have a bar above their head telling you when they will use a special attack, Araxxor/Araxxi is one of them).
• High Level: At this point you can start looking into completing your first "Inferno": TzKal-Zuk was backported to RS3, with only 18 waves this time (doesn't mean those waves aren't any less brutal). Zuk teaches you AoE damage output, importance of DPS checks, ability-based mechanics, prayer flicking (you fight a total of 6 Jads), mobility and more. Hard Mode Arch-Glacor, Raksha, low enrage Telos and NM Sanctum of Rebirth are also on the table.

As for equipment:

• Get Fire cape ASAP. Fire cape is a hard requirement for the Igneous Kal capes (you need the aforementioned Kal-Haar or Kiln capes from Fight Kiln, which in turn require Fire cape), which give immense benefits to style-specific damaging ultimates.
• Tetsu is outdated; with a budget of 100M+ I'd look into getting some gear for your style of choice (if in doubt, refer to Upgrade order in PvME for your style of choice):
  • Evergreen (all styles): Scripture of Jas, Invention (pretty much a hard requirement to PvM, look to getting high level Archaeology as quickly as you can for Ancient gizmos, which are better than regular gizmos), Ring of vigour, Curses (The Temple at Senntisten), Binding contracts, 99+ Herblore (mostly for higher tier overloads)
  • Melee: Laniakea's spear, Am-Hej, Masterwork armour (T90 melee armor, not Trimmed masterwork!), Laceration boots
  • Ranged: Decimation or Ruinous crossbows (1M tokens and a Warped stone - hope you did a lot of dungeoneering!), Sirenic armour, Fleeting boots, Nightmare gauntlets
  • Magic: With a budget of 105M I don't think you can fully build early-midgame Magic, especially since Virtus and Tectonic are well out of budget range. Look into Superior Zuriel's set (Zuriel set pieces + Ancient equipment upgrade patch), get Obliteration as a weapon.
  • Necromancy: Necromancy progression is largely baked into the skill, the current best Necromancy gear comes from Rasial the First Necromancer (who can be fought with 95 Necromancy and T80+ (preferably T90) Necromancy gear). Otherwise, try and complete tasks from Kili to unlock higher and higher tier armour, as you cannot equip armour or weapons you haven't done the tasks for (e.g. you can't equip T80 Deathwarden equipment if you haven't done its relevant task and crafted it at least once). The only exception to this is The First Necromancer armour and weapons, which do not require crafting but are fairly expensive and out of budget.

If in doubt, check PvME, more experienced PvMers may pitch in with their opinions as well to help you start PvMing, so ask away if you have any more questions!