The answers to both of these all depend on what continuity one is referring to.
technoshaman wrote:First one is where there any animal/bestial pre-earth cybertronian forms in the mythos? Or were they all vehicles?
In the G1 cartoon's first episode, Laserbeak had a sort of "bird"-like form before coming to Earth, and it differed from his Earth bird form.

In the War Waithin comics, which are set on Cybertron before coming the arrival on Earth, Trypticon has a saurian form.

Some characters have had animal-based altmodes even before their coming to Earth, though a good majority of these characters were conceived at times in which the current story had already succeeded the point at which the Transformers made contact with and arrived on Earth.
To make a long story short, yes there are some cases where pre-Earth Beast modes exist, but they aren't that common.
technoshaman wrote:Are there or have there been an cybertronian-type plant-life on Cybertron?
According to Beast Machines, yes. But it may not be the same answer elsewhere.