Seeking advice regarding buying a telescope I'd like to buy a telescope with a focal length of 700mm and an aperture of 60mm. 

Would I be able to use a telescope of this power to study the closer planets (for example Mars and Venus) and nebulae?
All the magnifications listed above 84x will be useless on a 60mm telescope.

Still, such a telescope can be useful if it is well made (particularly a steady tripod/mount) and you have reasonable expectations.

It will show lots of detail on the moon.  You will be able to see the phases of Venus and Mercury (which is pretty much all anyone can see of those from Earth).  You will be able to see Mars as a disk and maybe glimpse an ice cap or a little surface detail under excellent seeing with a favorable apparition.  You will be able to see Saturn's rings and Jupiter's moons and maybe with good conditions a band or two on Jupiter. 

It will only show a few of the very brightest nebulae, and only as a faint smudge.