I think you should only be able to craft base weapons, and possibly you tinker at high-levels (since the max will be 50, level 35 at least) to give items modifiers (like Keen or Fierce), with the maximum item you can modify is 5-10 levels lower than your overall level. You get slight exp for modifying, and medium EXP for crafting.
However, your tinkered modifiers can be increased, but at great cost and resource expense. For instance, you could get a normal Spider Fang Dagger and tinker it to make it Keen (+1 INT). For more materials and Mushcoin (at least double the inital tinker cost, so to make it +2 INT from +1 INT it would take 2x the materials to put it on there initially). The modifier caps out at 15 (no supra-godbows people), so you can’t make weapons too overpowered. You can still get dropped modifiers, but they cannot be upgraded.
I’m going to show you all an example of how this would work, using a Spider Fang Dagger with two Basic ATK scrolls on it AS EXAMPLE ONLY. Modifiers go from one to fifteen, in Roman numerals in the phrasing “Tinkered [modifier type, only Keen, Fierce, Vibrant, and Swift can be used] [Item Name] [Number of successful scrolls] [Roman numeral for how many items it has been tinkered]”
For example, a Spider Fang Dagger with three scrolls on it that has been Tinkered to be Keen four times would read as “Tinkered Keen Spider Fang Dagger +3 IV” and would give +4 INT. Any equipment can be so modified, but for increasingly high amounts.
For example, to upgrade a spider weapon the first time, it would require 30 Spider Fangs, 3 of the appropriate stat potion, and 500s. The second time, it would require twice that much (60 fangs, 6 of the stat pot, and 1G), The third, thrice as much. And so on and so forth until the final upgrade of XV (fifteen), by which point a spider weapon would have been invested with a grand total of 3600 Spider Fangs, 360 of the appropriate stat pot, and 60G Mushcoin! For Moko/Tuaa weapons, the item would be Mogomelons, and such forth.
To tinker with an item, you have to go to a special NPC in one of the city-type areas (Mushtown, Nilgarf, Port Fidelio, Warrior Stronghold, Tree of Life, and T3+ Guild Hall) called The Tinkerer. He offers to tinker your items as detailed above. There is NO going back on Tinkerings, meaning that you’re stuck with them forever. You also cannot have multiple tinkerings on a single item (no Fierce Keen Vibrant Swift weapons for instance), nor craft other modifiers.