Organic Polytunnel/Greenhouse 1st time outdoor grow tips & tricks needed.

[Big-D]

Hello my fellow Organic greenhouse growers, This is my 1st time doing an greenhouse grow as we now have the outdoor space and the privacy. I need to know the basics before the growing season kicks off in about a month here in Mid Wales UK. I have grown organic indoors with good results before but like i say im new to the outdoor.
.Anyway i shall start with my greenhouse i brought it from Ebay for £50 its 3metrex2metre so i imagine thats enough space for around 5-6 plants? It's made from a green plastic material and does have windows for air flow, its not glass so maybe a different approach to my grow?
.I have 4 25L airpots and some smart pots.
.My favourite soil is B&Q's multipurpose so i will try to use that or something similar.
.As for nutes im not sure what is my best option for an outdoor organic grow?
.Our garden is safe but there is a few walkers that go above our garden everynow and now & then so i was thinking maybe some frosting spray? also do you spray it on the inside or outside?
.As far as the lighting goes how do you control the veg and flower stages with 18-6 & 12-12? or do you just leave nature do its thing?
.i've heared its all about the strain and most early strains are best for uk greenhouse grows, however i have some seeds left from when i was going to grow last time the strains i have are: Blueberry, Lemon skunk, White Kush, Cookie Kush & Early Widow. Will those strains be suitable for my grow?
.Any other important info will be of a great help!
Peaceeee

[Yekke]

A thermostat controlled vent will be a huge game changer. You will also want a fan to avoid mold.