can one subtilise him/herself into particles/energy/elements to travel faster?

No

Possibly with advanced technology, such as matter-energy transporters/teleportation equipment. I used to think this was not possible, but then realising Astral Technology, perhaps it might be possible one day. If you want to go see somewhere, you could go out-of-body and travel wherever. There might be dangerous places to travel, though. I am referring to a member who said that before they came to Satanism, they went out-of-body and visited some DUMBs, and there were some sorts of barriers to block them from entering. I am not certain about Astral travel itself, but I do know that sending energy Astrally is instantaneous, regardless of the distance, so I presume that travelling Astrally is also instantaneous - but I am sure everyone, at least for a while, would want to actually travel instead and see the sights along the way.