Question/s about legendaries and crafting.
Different legendaries require different crafting check out the ones you are interested in on the wiki. Also will give you more of an idea of materials needed, dungeons needed to run, WvW track that needs to be finished and total gold if you just want to buy instead of taking time for the materials to accumulate. GW2efficiency also gives an option to use what is in your inventory to see reduction in costs.
The short story is that it’s worth looking up the specific legendary that interests you on any of the wiki, dulfy, gw2bltc.com, or gw2efficiency.com — they each give you different perspectives on what’s required and you can plan accordingly (one site should be sufficient — only look at others if the first one you choose is hard to read; everyone has a preference).
Generally speaking, leveling up crafting is expensive and only worth it as a long-term exercise. Most of your immediate needs can be more easily met by the TP (and for comparable costs, if you include the value of your time and labor).
The HoT legendaries all require the core Tyria mastery in Legendary Crafting. The generation 1 legendaries can be forged without it, if you buy the precursor from the TP. (Taking into account your time and effort, costs are “similar”.)
Technically, the precursors are “collected” — that includes scavenger hunts, FedEx/DHS quests (‘find this, take it to that to zap it, and bring it back to the other place’), perseverance tests (‘do these tasks’), kill 10 rats/kill a rat of unusual size quests, and yes, some crafting. The crafting usually involves the same discipline that would be used to craft a regular version of the item (e.g. artificer for staffs, huntsman for bows), but sometimes is more complicated.
However, your choice of profession (engineer in your case) needn’t have anything to do with your choice of disciplines (huntsman for example). My mesmer does my armorsmithing and my thief is an artificer — I just transfer stuff via the bank when needed.
Leveling up weaponsmithing/huntsman/artificer is relatively cheap these days. Around 100g total for getting to 500.
Additionally if you are going to craft a precursor the tier 2 collection gives you a recipe that makes getting from 300 to 400 cheaper.
In the case of weaponsmithing there is https://www.gw2bltc.com/en/item/77163-Vile-Jar which makes it even cheaper.
What I am getting at is that if you are going to craft a precursor and you don’t have the related crafting profession leveled yet you might want to wait a bit and use those recipes(especially the tier 2 thing since you have to craft 250 anyway).