I'm willing to take on questions for the RMFRP Treasure Companion since I use it in almost all my RM games lately enough that I know it almost by heart.
To answer your question on Work XXX spells, their main use is for enchanting magical items. For example, if you are making a highsteel magical sword, you would need both Work High Steel from Inorganic Skills which you were quoting and one of the weapon enchantment spells.
However you seem to be implying creation of a high steel longsword, which I assume is non-magical. In this case, you do NOT need the creation list. Refer to the section which deals with the bonuses that non-magical materials of all types give (can't quote page since my book isn't next to me, but its easy to find since its before the enchantment section, and it has a bunch of small tables). There, you will find the bonus for the material (high Steel is +10nm), the cost multipler (x50 iirc) and the difficulty to the crafting skill. In other words, a character with Metalcrafts would refer to that table to find out the difficulty for working the metal (which is a separate check than creating the weapon type).
However, if you don't need the spell list to create a non-magical weapon from High Steel, that doesn't mean the spell list is useless if you are doing just that. Using Work High Steel you can forego the crafting check and know that your non-magical sword will be flawless, which is nice if you're not that accomplished a crafter. Likewise, Make Steel will be useful if you don't have access to ready-made steel ingots.
One last clarification is that you don't need the multiple spells to work one item. If you're working an item made out of high steel, you don't need to cast for example Work Iron and Make Steel before casting Work High Steel. You just need Work High Steel, period, unless once again you don't have the steel made, in which case you would use Make Steel before starting the crafting. The only time where you genuinely need more than one spell is if you use different materials to compose the same item: Such as the Wood & Metal weapons, or if you are making a jewelry you might go with Work Base Metal for gold & work gem if you don't have the skills. And keep in mind that the spells insure that the items are made flawless and capable of being enchanted, but don't substitute themselves for skills if you want your work to have an artistic value.