no this is a great wattage light i just dont suggest the hood or the ballast, i would suggest a electronic ballast and an aircoold or cooltube hood hps lights throw off sum heat so youll need sum great ventilation and what more than an enclosed hood hooked to a 6 to 8 inch inline.
400w for 4 plants is plenty....What you need is an MH conversion bulb for the first month then switch to the HPS for flowering. So look for something that offers a MH conv system.
Yes, that would be great, but a MH conversion bulb for the first couple weeks is best. You can do it just read a lot online and go for it so much enjoyment out of growing your own smoke.... Have fun