Welcome Pablo. I can help with answers to some of your questions, but I've never played a Darling, so I can't answer questions specific to that model.
Alembic builds all their guitars and basses individually, almost completely by hand, so there is a great deal of flexibility when it comes to custom features. I'm sure you can order a Darling with no fretboard inlays, and LEDs are not standard. Headstock size and configuration is almost always customizable, though may involve an upcharge depending on what you have in mind. According to the Little Darling product page, the average weight is seven pounds, and I believe it's considered somewhat petite, compared to many guitars, so I would guess this makes it fairly easy to travel with. Alembic offers the California Special guitar with a tremolo unit, so it may be possible to have a Darling built with one as well.
I agree with Tom when it comes to versatility. I've owned a Skylark for two years, and I am still surprised and amazed at the variety of tone I can get from it. It is extremely clean and clear, and yet various combinations of the pickups and filter settings can produce enormous character.
Some of the other members here can discuss the physical characteristics. Jonathan (jalevinemd) owns the first Darling-like guitar Alembic built, from what I understand, and can fill you in on ergonomics. Other club members have played a Darling guitar at the Alembic shop, so hopefully they'll chime in too.
Best of luck.
Peace
Tom