This post is long, because it's going into some deep analysis, and asking you some questions which might help you figure out what you want from the character.
There's a difference being the House's go to Enchanter, and the House's go to Enchanter for specific items/effects. Let's face, it, I'd think it's pretty likely that House Mercere turns to House Verditius for a lot of enchantments. Now, can Antoninus fill a niche that a Verditius doesn't? Certainly and totally possible and reasonable. Niches can be very profitable for the individual.
Philosophic Alchemy, when you are looking at it to augment your MT score to try and handle more vis in a season isn't all that great. It's governed by your CrVi Extraction total, and Creo and Vim aren't Antoninus's specialties. Let's look at his CrVi Extraction total (Cr 8 + Vi 7+ Int 2 + MT 5 + Aura 3) of 25. That's 3 pawns. He can move to Eilon Chon, if the lab is available and add 12 to the total for a total of 4 pawns. Getting to 5 isn't all that far off. Let's say that Philosophic Alchemy adds 5 pawns to just round it out.
Let's run this further out, and move your MT score up to 6, since we have a summa and you can get it to that level in a couple of seasons with a Q15 book. Let's also say that you've acquired Major Philosophic Alchemy. And also let's say that you change your specialty for MT to Enchanting, making it an effective 7. So now, for the bulk of Antoninus's career he can effectively handle 19 (5 from Philosophic Alchemy and 14 from an effective MT of 7) pawns of vis when opening a device, working diligently he can probably get that up to the mid 20s by the end of his career, but probably not much further than that. Having an able assistant will push his CrVi extraction total up, having a customized lab will help, but when you're dividing a CrVi Lab total by 10, it's not a lot of vis that you can add. And, to top it off, it requires an extra season of work and some pre-planning/effort. So for 2 seasons of effort, you can probably handle opening a device with 19 pawns of vis. Yes, you can do something else during that season where you're pre-staging 5 pawns of vis...still requires the planning.
Vulgar Alchemy has some problems and was recently discussedon the main Ars forum. It certainly doesn't add much, IMO, and is definitely unwieldy as written. I don't believe Vulgar Alchemy is at all necessary to initiate Hermetic Alchemy. Why not skip to Hermetic Alchemy, unless there's something in Vulgar Alchemy that you really want? And I personally don't have an issue with you initiating Hermetic Alchemy or Vulgar Alchemy with some kind of sacrifice. I think you were on this path because of The Order of the Green Cockerel, perhaps? I'm recalling that from memory, so I might be wrong.
All that being said, Talia is very interested in these Mysteries (or will be when she hears about them), too, so if Antoninus is interested in having an amica following a similar path, Talia is one to be there. And I wouldn't mind, personally, as a player, developing and/or exploring a mystery. Talia does want to enchant a ship, but she has some advantages over Antoninus, four to be precise: Puissant Creo, Affinity with Creo, Pussiant Magic Theory and Affinity with Magic Theory. I don't say that to discourage you from the journey you want your character to take, only to emphasize that what you think you're gaining from it may not be as much as you'd like.