240V Electrical Questions, power multiple welders,plasma

I build a cart for my Mig, Tig, Water Cooler & Plasma Cutter.
I got ahold of some old 1930's steel cartwheels. So I decided to Fab up a two-story cart with a roof and side walls around the framing. Anyway, I was hoping to Power the cart. I have the outlets and wire needed for the cart its self. I was wanting to add an additional Nema 6-50 in the case it is needed. I also wanted to have 4 Nema 5-15 outlets for tooling. So the card would have 4 Nema 6-50 outlets and 4 NEMA 5-15 outlets.
I was thinking about attaching a 12 space 24 circuit subpanel right two the cart. However, finding the right 30' cord to run to it is proving to be a challenge. I will only be powering one of the units at one time. Max input/rush amp rating for units are as follows (Mig 48A) (Tig 41A) (WC 1.1A) (Plasma 40A) So I started to think I can put a 125A subpanel run a 50Amp cord from the 14-50 wall outlet to the subpanel Drop 3-40 amp breakers in the subpanel and 1- 50amp breaker & 2-20amp for the 5-15outlets using them as on/off switch at the same time. making sure to only run one unit at a time.

If I'm looking at this wrong or anyone has a good idea I'm willing to listen. My goal is to not have to run 4 cords from my cart. but to only run one cord from the cart to a wall outlet or wall outlet off a new subpanel if need be to power all the equipment. However, One at a time is fine by me as I can only use one welder or plasma or power tool. It will be a lot easier to flip a switch then unplug and plug in every couple of min. I have pics of the cart build as it is still in progress. Framing is complete starting to find the locations for outlets now.