about 3 feet tall is right, but you can control height easily by simple training.
1 gallon reservoir is too small.
spacing is not something that has a standard. many prefer crowding as many plants as possible, knowing they might not thrive as much,…but the quantity of plants compensates for that. others prefer to not crowd and allow more ventilation and light energy to help plant thrive. personally, i prefer the latter. but im sure you can find just as much support for the former.
here is pic of 4 white widow. these are day 28something of 12/12 lighting.
they are in 5gallon containers with soil. but you can get an idea of mature size.
i did “top” all 4 of those plants. reducing height slightly and producing more “tops”
here is link to my recent White Widow Journal
hope that helps.