when the bomb goes off that thing will be the only thing standing lol overall i think youll be fine with some minor adjustments
would suggest a couple things maybe add some braces on the top 2x4 is fine
add a 3/4 sheet of plywood to the top or something similar in thickness
i would also brace the bottom and cover it up so its not bare floor
you dont need very large or heavy lumber for the framing small piecs like 2x4 and 2x6 can be all you need if its tied in right when everything is together it should hold most weight of anything you could ask.take in consideration the weight and size of your stand when its done and if youd ever want to modify it or move it it woulkd be difficult