Need help about lighting from experienced indoor tent growers

Here is a bit about the setup:

I have a 2 width x 2.5 length x 5 height grow tent.

I have decided on growing 2 plants of BC Big Bud which can grow to about 4ft-5ft I have heard.

I want to use MH for veg and HPS for flowering.

Should I go for the 150 W 250 W or 400 W for the MH and the HPS?

Also what kind of ventilation should I be going for? Ive grown once before with this grow box with 150W HPS and used 4 computer fans. Would that suffice if i increased to 250 of 400? Also how strong should the computer fans be?

Please help, I would really like to start preparing my grow.

peace

Originally I was wanting to go 400W MH / 250 HPS however I realized the grow box is a bit small and could get a bit too hot. Would this set up be fine or am I at risk of going overboard on the heat?

common, anyone?

veg. 2ft 4bulb t5.
flower 250w hps.

if u stick to cpu fans, get a few of the highest CFM you can get.
I would personally go for 2 250+ cfm duct boosters. 1 intake 1 out.

id probably go with 150w mh then to 250w hps

depending on your exhaust system and the temperature outside the tent i think a 400w would get to hot