Are there any guidelines for the above?
Whether I'm talking about Adamic, Enchanting Music, Dousing or Heron's Mechanica, is there a system limiting these at chargen? Or at least is there a system to detail the difficulty of learning these while in apprenticeship?
For example, technically, other than the troupe, does anything stop a 25 year old verditus from having Craft Automata? what about Mechanica of Heron?
Thanks
Take a look at the apprentices subsection of the laboratory section in ArM5 to see how difficult it is to open and apprentice's Arts without destroying their Supernatural Virtues. Then look at the advancement section in ArM5 to see about learning new Supernatural Abilities. The book Apprentices doesn't really change anything in regard to these; rather, it explains similar ways to acquire Hermetic Virtues and Flaws.
Chris
There is nothing that really limits this at character generation, as if starting from scratch. However, if you reverse the process and see what is necessary to preserve these virtues under RAW from the 5th Edition text (page 107), whoever opened the Arts had a very high InVi lab total to preserve those virtues. This could lead to a master hiring another magus to open the Arts, with a contract specifying payment, etc. If you're using Apprentices, you can create magi from the ground up, but need to know who is making the magus to be, to some extent.
Craft Automata is a Hermetic Virtue, not a supernatural virtue, though, and is an Inner Mystery, which requires advancement through the House Verditius mysteries to be gained. It would be unusual for a Verditius magus to pass his gauntlet with this, but not necessarily unheard of...
Mechanica of Heron is a Supernatural Virtue, to open the Arts of a Gifted person with this virtue, one needs an InVi lab total 5 times the score or at least 30 (whichever is greater), but this destroyes the virtue. To preserve the Virtue, you need to double the amount. Multiple Supernatural virtues increase the InVi score necessary in an additive fashion.
For Adamic or Heron's legacy there is the clear limitation of AM p.6 - saying that "there are no living practitioners for Hermetic wizards to learn ancient magic from, to assist them in understanding the golden age lore, or to advise them in the way of finding the lost secrets." So that's an obvious no no for starting characters, unless the troupe wants to play a very special campaign and hence removes the limits.
Dowsing and Enchanting Music, on the other hand, can be built into starting characters, also starting Magi characters. It might be wise to incorporate them into the character background prominently, though.
Craft Automata at chargen of a Verditius requires a character background where an initiation into Verditius Inner Mysteries could have already occurred, and appropriate other Virtues, Flaws and Hybris score.
Cheers
Short answer: yes, there is a limiting factor to how many supernatural abilities you can have at chargen.
Since a magus does not meet the criteria of the second sentence (they fail the 'who are not magi' clause), they are bound by the first; they require the virtue.
With regard to Ancient Magic or The Mysteries, you will need troupe approval before taking those virtues. As written (and as others have said), they are not designed to be stuff to begin the game with.
I can only think of one scenario where I would approve such virtues at character creation: if the saga has been running for a very, very long time and the troupe has already done the adventures and earned the treasure!
It's also realistic to have advanced Mystery Virtues if the player characters are old when the saga begins. (Although, of course, precisely which ones are available might be a question for the troupe to consider).