Non-existence

[LukeMC]

That is not a necessary premise for solipsism, no. All it states is that your conscious mind exists, and it's conscious experience. It doesn't state that anything that falls outside your actual conscious experience exists even in your mind, because to state that would be unverifiable. And since it doesn't state that your sense-data exists independently of your conscious experience, the sense data itself, even if it was much larger than it is, will always be less complex than an actually existing reality, since sense data contains and records less than actually exists according to realism.

The reality itself would be less complex, but not the whole system. Of course, if all I'd ever seen in my life was my bedroom, it would be much simpler to say my bedroom is all that exists than to say a universe exists outside of it. But the difference is that (like Kyuu said) the idea of a universe offers one or two layers of complexity to exist, whereas a conscious mind upholding its experience of a universe it created adds whole new layers of baffling complexity to the system as a whole.

With solipsism I can go as far as to say my mind is real and what I cosciously experience is real in one form or another. After this, the assumptions I base my life on are not to do with solipsism as such, but stem from an Occam's razor decision of which scenario is the least complex/most probable. With my confirmed conscious mind I can go on to conclude that if my mind is all that exists, it must have greater levels of complexity to process the experiences I have had than whatever complexity an objective universe has. By no means am I claiming this to be verifiable. Just a foundation built up from the first premise.

Not according to the doctrine of divine simplicity, the orthodox Christian understanding of God, which explicitly states that God is the simplest possible being, and that all his attributes are identical to his being, and that the universe is more complex than God.