Slitherine

If Germany stays out of Belgium does Britain stay out of the war?

No, but they will join a bit later.

To attack against Maginot line was not possible for German. So the only way was Belgium or Netherlands (if they wanted war).
But the problem of England is not so easy to imagine.
For Germans to cross Belgium was the way to go the faster they expected. But they ignore Belgish hard resistance. They even kill civil residents.
Wars was in this way not changed.

There was no Maginot line in 1914. Germany could have attacked at the border they share with France. Going through Belgium was maybe a good tactical move, but forced the UK's entry into war (as they had guaranteed the safety of Belgium).

In 1914 in France it's the Séré de Rivières system. Set of fortifications built from 1874 until the beginning of the First World War along the borders and the coasts of France[/b]

That is why German plannification also discounted a French attack from that area, since that would forfeit the advantage of the fortification system. Ironically, plan XVII devised exactly such an attack. This attack was easily defeated in August, but again ironically that same German defensive success led to failure, because they tried to exploit the defensive victory in that sector pressing the French, that took shelter in the lines of fortifications. German succesive attacks were bloodily repulse and reinforcements sorely needed in the right wing moving through Belgium were committed to this battle.

BTW I imagine that if Belgium is not attacked by Germany it will remain neutral, and if it is attacked by the Entente it will realign itself with Germany, right?

Yes, and the latter would stop the UK from entering the war (if they haven't already).

And what about Italy, what are the conditions for the entry of Italy in the war?