I was going to do the same as you when I had my 125g
A builder aquaintance suggested a 1/4" steel plate of 6x6" or larger under the jack post
The wood you have under it may split and could be a bit larger to prevent the concrete from cracking (it is a concrete floor, ya?)
I also talked to an engineer. Because of the cost of liability I didn't pay him for his services. He told me he entered my flooring and weight specs into his formula and told me that, if I were to pay him, he would suggest the above idea as a minimum, but because I wasn't paying him, he wouldn't be legally allowed to tell me that
The rest looks great. All I'd add to it is some cross bracing between the new support joists to prevent twisting