Should I cut the bucket down to give airflow and a...

No don't worry, everything will turn out fine. But yes, always fill your containers right up to the top!

and, lol i thought it was some translation error.. no i wouldn't cut the bucket down.. if you have some air currents, it'll be fine. remove any leaves pointing down into substrate.. if you really wanted to, once it's taller you can add an inch or two of substrate if you wish.. i wouldn't bother though. When you transplant, before you bury anything, place the put into the hole you dug... is it at the right level? if not dig some more or fill it in a bit to get it to the right level. i try to get a layer on top of the transplant. if you ahd good watering habits, you shouldn't have any superficial roots, so removing a 1/2" off the top of a transplant isn't too big of a deal either -- one more tool to level it out the way you want. When i transplant a larger plant in a 1gallon (vs seedling pot), i dig a partial hole with a slgihtyl udnerfilled pot. this way i can level it out and work the substrate around it to hold it steady exactly where i want it - e.g. if tilted i gently lift it and push some substrate under or pack in one side to hold it more vertically. Once sufficiently positions, then pour in some from sides to fill in the rest... hold the leaves up with one hand and dump it in, then level it out. Jst work your way around. this part doesn't take much ... dump and level. I do one half then the other. Make sure if anything is not even it is concave and not convest.. between the two options - water you put on top rolling (gravity/slope) toward center is better than toward the edges. It makes watering more of a pain to ensure no dry pocklets if ther's a slope or uneven top... the low side will sink in faster / gravity will pull it that way as you water the top... i have a sloped platform.. i slightly favor the high side with my drippers for this reason.

It doesn't look like the nodes are too tight. slow growth could be from genetics or the substrate if not the best... even the balance of nutes -- though in regard to nutes they look fine... probably just a bushy, short plant.

In that situation, i sometimes remove leaves pointing inward if they are all bunched up.. try to alternate what you remove so that 1 limb doesn't take more damage than the rest. if you have an idea on how large you want the plant to be, these early nodes may not even be important or used later on... in those cases i might prun them off or strip lower axillary buds (leaving the leaves as much as possible). if it is unused growth later on, no harm removing it now. Try to retain as many leaves as possible, though. my threshold for removing a leaf is if it's all controted and unhealthy looking. They go downhill in that context.. slowly pale and shed by plant. Contorted leaves are trying way too hard to find light or breathing room. Shielded leaves are still a net positive for the plant, however. they still store necessary building blocks. They still bring in CO2, the limiting factor for growth in most gardens. A useless axillary branch is a sinkhole for resources, but leaves are useful almost always as long as not physically bunched up beyond reason. If your node spacing is very tight, try reducing light intensity a bit and see what happens over enough time. If it is stunted at all, the longer it's been stunted the longer it takes to snap out of it. Minor stretch early on is not too big of a deal. It helps spread the plant out and avoid this situation. Have an end goal for your plant as far as area of growth and number of colas. Work backward from there to form a plant to shape the plant in the most efficient way to get there. Doing so gives clarity on what is needed growth and resource wasting branches that'll never be used. This isn't fool-proof, and soemtimes you leave excess when unsure or need clones... i recently stripped all my lower nodes as they got large enough to pluck, forgetting i needed to take cuttings before flower phase, LOL... looks like i'm taking cuts in flower, oops. Point is.. have a plant. think it through. Only cut off what is not needed. Have a good reason to remove leaves, if you do. A little trial and error to find out where that threshold is and to gain familiarity is a rite of passage.