If you picked up a running Space Saver for $200 you got the deal of the century!!! Starting out on one will be a great thing.
Most people start with an 8" or 10" wheel. A small contact wheel is nice for some inside curves. 1.5" to 3" is a good size. There is always a debate on smooth vs serrated wheel surface, but most start with smooth.
Your 14" soft wheel may be very useful later on, so hang on to it. If you don't think you will ever use it, send it to me ( just kidding).
What you will really want is a flat platen. Places like Oregon Blade maker and other Ebay sellers have them at reasonable prices. Some of those flat platen setups have a 2" and a 5" wheel on them, so they kill three birds with one stone. For a starter setup, these can't be beat.
If you do a lot of work with guards and shaped finger grooves, eventually you may want a set of small wheels and a small wheel tip. These usually cover .5" to 1.5". They are not worth it to a new or small time maker, but are really nice for those doing production level or fancy shaped knives.
Some folks panic over the 132" belt cost, but remember they last twice as long. 132" is the standard for industrial belts, so any belt made in 2X72 is also available in 2X132.