well you did the right thing for using hps for flowering and mh for veg. as for your exhaust problem. veging process doesnt need as much exhaust as blooming does. i think you should switch the 250 cfm with the 110 cfm in your bloom room. this way the humidity lowers and prevents bud mold and other mold. You really dont have to worry about much for vegging. just put one exhaust fan for vegging and no input fan. (use the 110 cfm for veg exhaust.)