Don't invest in command for a 10 man unit of halberdiers. That's a waste of points. If you are going to give them command, I'd bump them up to being at least a 25 man unit. Then as you'll have 5 extra statetroop models, bump the swordsmen up to 25 as well.
As I recently experienced in a 500 point game, it's really tough to make a good list for all comers. If you were ever to face a Warriors of Chaos army, a big unit of Marauders with Greatweapons and the mark of Khorne will eat this list for lunch.
I'd say drop the cannon and go for a Mortar. It will be of much greater use in a 500 point game. A big horde will be much more difficult to deal with. That's not to say that there aren't any other tough units that a mortar will have a hard time with, but I think it's the best compromise at this points level.
So this is something I'd consider.
Captain, Fullplate, Shield, Sword of Power, and Ironcurse Icon (105 Points)
25 Swordsmen, Full Command (175 Points)
25 Halberdiers, Full Command (145 Points)
Mortar (75 Points)
The only thing this lacks is good magic defense, which will be really tough for any army to deal with at this points level. Fortunately an opponent will be extremely limited in his magic offense as well due to the 125 points restriction on heroes and lords.