dont bother wasting them tight funds on other foods yet,. they actualy use more nitro in bloom than the other 2. we test this weekly to see what they use more or less of. old thinking they need more phos and potassium. google the phosphorus myth by advanced nutes.
your at 18 inch now...ya flower em. they may go 3 x that hight. and a 600 only has max lumens up to 22 inches from bulb. 1 more inch is 50% less lumens so is a waste of veg time and foods to go taller. you dont have enough lighting for it.
ya looks male kinda to me. i only see 1 ball set and usual;y is more. they will show sex in veg or any light once they reach maturaity. they do show faster in 12/12 lighting though. and slower under less light.
rotating them is fine to do also.
bigger pot dont make for a big diff in size. i have some in 1 gal and 2 and 3 gal and there is so little diff its hard to see. all you get is a bit more lateral branching,. average rule is 1 month age 1 gal. or 1 foot hight to each gal. longer veg makes for bigger plants. ive run in solo cups and got same as in 2 gal pots in my past to show others this....5 month in a cup.
your crushing the stem is called pinching. it temporary re-direct the hormoes. not like topping does. its sorta a form of Lst, gently roll in fingers till oyu feel the pulp crush then leave it. or bend over if hight is an issue.
a 600 in 4x4 is just right. dont cheep out on a fan though. like dont use a pc fan or think it will coll enough for you. if money is tight look at a squirl cage fan, probably the cheepe3st and most cfm for your buck. other than a real exhaust fan