Thats heaps you need about 1 gallon (3.8 litres) pot size per month your plant will be alive... so a 5 month grow you should have around 19 litres or 5 gallons atleast. But the more space the bigger your plants will grow. You only have to worry about being rootbound when you are under those numbers.
Is your yates insecticide organic or synthetic? You dont want to use any "in-organic" sprays on them when they are flowering as it is harmful to smoke buds that have been sprayed and they probably wont taste the same.
For some reason mites can develop a resistance to insecticides so the first 2 applications might wipe the adults out but then the next generations will become resistant meaning the insecticide will become useless
The neem oil I used last year did really good (better than insecticide for spidey mites apparently), all you need is 1 application every 4 or so days and treat it for around 2 weeks until all mites and eggs are destroyed, just rinse it off the leaves afterwards with plain water, try not to apply anything during flowering but if you have to, the dish soap with luke warm water method maybe better as to not spoil the taste of your buds!
Mites do love dry (low humidity) and heat so if it hasn't rained in a while just spray leaves with plain water in early morning or evening (to not burn the leaves) as it helps keep them from coming back because as they say: prevention is better than cure!
Goodluck!