You can work on them both at the same time as long as you only test pH when the chlorine level is below 15ppm. When the chlorine is any higher than that, you will get a falsely high pH reading.

You will need to replace the pressure gauge and you don't need hubby to do it. You can pick one up at any pool store. They are pretty cheap --- around $10 or so. The only thing you have to do is unscrew the old one, put about 8 turns of white Teflon tape (get it at Lowe's etc. or the pool store will have it but just more expensive there) around the threads of the new one and then screw it in. Easy.

Who knows how much bleach??? Just go to Walmart and load up a buggy with as many as you can hold. With this big of a pool, it will take a lot. Maybe even take someone with you and get two buggies of bleach. Initially, while the pool is green, you'll use LOTS. Then, as it clears, you'll taper down, but will still use several gallons a week with this big pool.

Don't worry about the Frog. Ever. Just unhook it and don't use it anymore. Just use bleach for your chlorine.

Regarding type of brush -- I don't know. Probably wire but I don't have a gunite pool.

Let us know how it is going and if you have any more questions, ask away and we'll try and help.