If you have the means to keep a 1k MH cool, then by all means use it! An MH is going to give you shorter nodes, which helps if space becomes an issue. If you're going to veg ten plants or more, the more light you can get to the leaves the better. And not quite sure what you meant in your last post, but I wouldn't recommend trying to run two bulbs off one ballast. You should also only use the type of bulb that is specified for your ballast... i.e. don't stick a 1kW bulb in a 250W ballast, even if the sockets match up. It won't work and could start a fire.