Hi, the best way will be to rapidly level up your mining so you can mine lots of coal in the mining guild. If you save your iron from mining in east varrock mine up until then, you should have some decent amount of materials for iron and steel bars.

Your iron-only scheme probably won't provide enough XP after a certain point, I do recommend you do some steel bars too. But here is the key, IMO this is the true protip:

Get your crafting up to 40 and grab a brown apron, so you can access the gold mine in the crafting guild southwest of Falador. (there is a certer added who will be able to essentially bank your nuggets). It's recommended you use the Gauntlets of Goldsmithing from the family crest quest to smelt your gold bars. Smelting gold nuggets into gold bars while wearing those gauntlets is most likely the fastest way to get smithing XP in the game.

The smithing xp comes from making gold nuggets into bars, however I think making the gold bars into golden bowls after completing legends is quite good XP as well.

But first i have to lvl up my combat. Lvl 121 demon for the gaunts quest is bretty heavy i think xD

Get yourself lvl 37 prayer to unlock the Paralyze Monster prayer , the lvl 121 gets super ez at that point . I belive i killed it a 60ish combat lvl.

If completing all quests isn't something you look forward to doing, keep in mind that smelting gold nuggets into gold bars could take you all the way to 99 without ever having to make golden bowls ... assuming you can mine that much gold

There was a fan-made app by Honour called RSCR Tools, I'm not sure if it's still updated but it could help crunch the numbers based on your high score information.