Hi, welcome to the community.
First of all, if you plan to keep using LE7 you need a computer over 10 years old.
Here's a compatibility chart for you. Using such computer may not be practical.
Second, you cannot use 192 interface with Pro Tools LE, that is simply put impossible. You would also need HD card(s) to connect such interface(s).
Third, I don't know what is "Channel 24" desk but I guess you mean either Control|24 (the older Digidesign branded) or C|24 (the newer Avid branded) controller. Those won't work with LE software either.
What you need is HD software, but before buying make sure you have the newer C|24 controller because the older Command|24 won't work with PT11 and later. Will work with PT10 though, and by buying HD software you get a PT10/11/12 license bundle.
So... you have lots to think and perhaps lots to buy.