Also, before I start, most people view tulpas as fully independent people, so you shouldn't refer to tulpas with it/its pronouns unless that specific tulpa is okay with it!
It's definitely common and often deliberately trained to experience your tulpa's voice internally (vocality), but it's not to the same degree as imposing your tulpa's form in the physical world. However, not all tulpas communicate via internal monologue and may communicate through things like images and feelings (tulpish), though this is often considered a precursor to vocality.
No, it's not required to be able to dissociate to switch at all, but most people believe it's needed to do more in-depth or complete switches. I don't have any links off the top of my head, but there are traumagenic systems who also have tulpas, but one thing I can tell you is that with switching with a tulpa, there is often little to no blacking out/amnesia and outside of extraordinary circumstances, it almost always consensual. That's something a tulpa and their host usually would have to train manually (memory separation), and it's often discouraged: https://www.reddit.com/r/Tulpas/comments/1l23eyc/psa_having_full_memory_separation_is_terrible_and/
Take me, for example. When I switch with my tulpas, I can choose to go unconscious, can stick around in co-consciousness, or spend time in a mindscape. For me, when I come back, I vaguely have an idea of what my systemmates did, but the details are lost on me unless I really focus on remembering or said systemmate tells me what they did. Like how yesterday, Arcanus apparently spent time rebuilding his music playlist, and I forgot he did that until he mentioned it/saw he left the folder open.
Regarding how fast a person can make a tulpa... there isn't a clear consensus, but some things that can play a role are:
Schizophrenia/Psychotic disorders
How much time you spend forcing every day or how often you force in general
It can take people as little as a day or up to years to create a tulpa, but I will say that how long doesn't necessarily determine how independent/fleshed out a tulpa can be. A tulpa made in a day can be as complex as a tulpa that took seven years to become sentient. Once a tulpa's developed enough, they can pretty much exist on their own without needing active attention from their host. For example, we have several systemmates here that are hardly active at all, but can choose to pop in whenever they like without any prompting.
The main theory I know of is the Mirror Neuron Theory where basically, you create a miniature neural network/cluster of neurons in your brain via Tulpamancy techniques that's basically your tulpa, but that theory is a little hard to believe because that implies "you" exist in a localized area in the brain when that's pretty unlikely. Tulpas can exist independently of their hosts, even if the host goes into dormancy/commits egocide. Unfortunately, research on Tulpamancy or non-traumagenic Plurality in general is incredibly scarce, so there isn't anything concrete. However, do keep on the lookout for an FMRI study Stanford's planning on releasing... eventually.
