OK, did some thinking:
1) I definitely want horizontal menu, it simply feels like "select subpage" the most.
2) I think I will have to resign from buttons being strethed to fit the whole width of the page. Especially since sometimes there might be only one button, which looks very ugly then.
The best I could think of is a separate box with centred plain text links... Not thrilled about that one through (probably will look ugly)...