Not planning in heavy rock/metal, but also not classic/jazz/blues.

Its first guitar with budget of 300 pounds. Shoud i go hss, hh or hsh? I am worried that hsh may be too heavy though.

Unfortunatly i don't have the means to test before buy so relying on your expertise.

Have pacifica 112 and squier fat strat standard as possibilities as of now. Any recommendations?

If your going for a clean sound most of the time and a sort of blur/oasis/lenny kravitz kinda rock sound, single coils should be cool. Humbuckers are generally preffered by some people as the out put is a little higher (depending on the humbucker). But they also give less feedback when playing live.
I use either a J5 Tele or a HH Strat which are both very versatile due to me playing a lot of styles.
Hope that's of some help