All source maps are made in hammer.
The grid for working area is massive for a MP map.
Unless your taking about the unit size, in which you press [ and ] to make the grid smaller and larger.
Here is a shot of a old version of Fac_bz (beta4 I believe) to show the size in hammer:
Bottom left shows that you can get the grids pretty small.
And of course if you can your best option is to model your props and such in like 3ds max them import. But you have to now how to model and texture for that. But for your first map, our supplied textures and models should be more then enough.