1. Here there's two kinds of mobo's available PH61 and PH67. Which of these is better and why?
for a i5-2400 the H61 is fine and probably cheaper. the P67 is a better board (more bells and whistles) and is for overclocking "K" series CPUs.
2. Does a HD 6670 deliver playable fps for BF3? and at what res can I possibly max out the settings with this card?
no, the 6670 will not play BF3 at 1080p very well even on low presets. even at 1280x1024 it barely achieves playable frame rates on low presets. I would suggest at least a HD 5770/6770/7770 or GTX 550ti/GTX 460 as a minimum to play BF3http://www.tomshardware.com/reviews/geforce-gt-640-review,3214-3.html
3. how do I decide on the psu for this config
depends on the quality of the PSU and what kind on GPU you will put in it. Generally I would lean toward a 400-500w PSU in any build.
what brands are available in your area?
good quality low cost PSU to look at.
CX 430W v2
CX 500W v2
Antec PSU should be fine:
EA 380D 380 w (very good and solid for its size)
any Seasonic, Silverstone, XFX or PC Power and cooling will be fine.
Some OCZ psu's are ok also
link to PSU reviews:http://www.realhardtechx.com/index_archivos/Page1373.htm