Can I use separate vbo buffer for every mesh or submesh or do I have to use bigger vbo’s and then save indexes to that bigger buffer to avoid similar performance loss I remember there is in DX vertexbuffers with many small buffers.
I remember I have heard something that vbo is planned in a way that it enables best performance even with many small buffers. Do I remember correctly? Thjanks 
You can use as many vertex buffer objects as you want. There will no performance hit if you build many little vertex buffer objects, and in some cases there could even be a performance gain.
With that said, there is an obvious case where it is recommended not to use VBO : when the vertex buffer objects are extremely small (say, less than 10 vertices). In that case, immediate mode is preferred.
Anyway unless you render millions of tiny objects like that, you will not even notice the performance drop by using VBO for those objects.