Sam,
I highly recommend 3D Canvas as your construction program. It is a very capable program, is relatively easy to use, has many train modeling plug-ins, and has a great train orientated support group.
This URL will direct you to a very good comparison of available programs.
[
steam4me.railpage.org.au]
A bit of advice though - start with a simple stationary model (like an outhouse) and work your way up. Learn to walk before you try to run. More people fail to become proficient because of trying to do too much too soon than for any other reason.
Bill