Trains on the Seymour line are usually an even mix of either Sprinters and Vlocities. There are also some locomotive hauled trains on select peak hour services (N class hauled H sets).
These trains run approximately every hour from Southern Cross, although services may be slightly less frequent on Weekends and public holidays, and more frequent during morning and afternoon peak hours.
On top of these 'normal' Seymour services, there are also the Intercity services to Shepparton and Albury, both operated by N class locomotives and N set carrriages. It should be noted though that Albury trains run on the Standard Guage (SG) line. The SG line roughly runs adjacent to the Victorian Broad Guage (BG) line used by Seymour and Shepparton trains.
Both Albury and Shepparton trains run 3 times a day in each direction. Yes you can use them to travel inbetween Melbourne and Seymour, but these trains don't stop at most intermediate stations especially SG Albury trains which run express inbetween Broadmeadows and Seymour.
All of this information is easily attainable with just a little looking around on the V/Line website.