Just updated
the first Steampunk post, to fix the crunch note: I realised that the Single-Minded advantage fit both the text and my intentions better than a perk or quirk would. Still not sure about the cost of the artistic limitations, though I'm leaning toward -10% for 'Only While Being Artistic', since Basic Set - Characters has 'Only while playing the trumpet' at -20%. Mind you, 'being artistic' in this context doesn't mean just using an artistic skill - might change it to 'Only while in a creative mood', but that's harder to judge.
Rather less sure about the correct cost of 'Always Activated when being Artistic' (which should probably be rephrased), as it doesn't mean that the Wild Talent activates more than once per game session per level, just that until the limitation is bought off, the character can't avoid activating it when 'doing art', unless the advantage is used up for this session. Suggestions, or should I pm PK for help? Don't really want to bother him for this, unless no-one else has a clear idea.
On another note, a clarification: many new thoughtforms that aren't bound to a fetish have the version of Terminally Ill which is unnamed but described on p35 of GURPS Spirits (under Spirit Weaknesses). In short, they must make a Will roll once a month, or lose a level of HT. If they reach HT 0, they 'die'. Most have an even stricter version, dissipating the first time they fail the roll. Really not sure how much either version is worth in 4e, but the former is probably close to the cost of 'Terminally Ill (Up to one year)' [-75]. This disadvantage can be bought off or reduced if the spirit lasts long enough, and 'eating' other thoughtforms will either grant a bonus to the Will roll, or allow the spirit to skip it. As they frequently have some version of the Mindless Spirit template on Spirits p36 (though usually without a taboo trait of 'No mental skills', because their tasks often require mental skills, they just rarely can improve them, nor learn new ones), they usually fail these rolls, due to having a Will of 8. Generally, it's the ones without the Mindless template that grow to become full spirits.
Also, it's rare for a new thoughtform to have any level of Astral Armor, unless they were created for a task that requires it (in which case it often has the Expansion technique, or a similar enhancement). More mature and powerful thoughtforms, like those that a PC might end up fighting, frequently
do have some level of Astral Armor.
A clarification on Dp-Earth's magic: when I mentioned Thaumatology: Age of Gold as a good example, that was specifically a matter of feel. It is not meant to imply that the magic system in Age of Gold is exactly that used on Dp-Earth. The traditions on pp17 & 18 are the most common Energy Accumulating styles, along with an adaptation of the Ritual Path Magic system from GURPS Monster Hunters (which is called 'Neo-Sephirothic' on Dp-Earth), but are not the only ones, nor is there a lack of Effect Shaping styles. Also, Path/Book Adept is certainly available to Dp-Earth PCs, at least in high-level games.