I just reach the level where I can craft ilvl 400+ gear for Blacksmithing and I was hoping that I can craft this high ilvl gear and trade it to my alts but I’m not entirely sure if I can mail my crafted gear to my alts.
Yeah if it’s Bind on Equip. Otherwise place a crafting order from your alt to your crafter character. 
As Waggle said, you need your alt to place a private order for the item with your blacksmith. That’s the only way to get items to another toon unless its Bind on Equip.