1-What class of planet do you use for each type of world?
Haven't given this much thought, in the few games I've played, they're usually all PQ 8-11, but mostly PQ 11. If it ever dips into the single digits, it's because it's been hit by an invasion or two, and as such, I use whatever remnant buildings to decide what type of speciatly I'll use. Haven't had to make a judgement call on a fresh lower PQ planet. Generally though, I'd only make a high PQ planet an econ planet.
2-Do you especialize your homeworld too?
Somewhat, I lean toward industry as it's the location of my sole starport for a while. Usually have an entertainment building, couple farms, couple econ, couple labs, then rest factories.
3-What Buildings do you use for eah type of world?
I start with a factory, and if I can afford it I'll buy it using the first couple options. Then I alternate between its specialty buildings (factories, econ, or labs), a couple farms, and a couple approval boosting buildings. May throw in influence buildings if a bonus tile presents itself.
4-What ratio do you use for industrial/reaserch and economic?
Don't have a ratio per se. I just go by what I need. Probably around 3/8 econ, 3/8 research, and 2/8 industrial.