Kinda hard to tell from the pic. General rule of thumb is 1 lbs per gallon. Of course, that’s not a golden rule. I’ve seen some tanks thrive with less and others with more.
Yeah depends on how big your system is my 5 gallon probably has about maybe 8 lbs in it but that all wet , generally your gonna want a lot of surface area so if you can get more porous live rock if possible
There really is no rule of thumb when it comesto rocks any more. This is mainly because there are so many different rocks out there that you cant use weight. A really porous rock will be very light compared to same size Marco rock which is a lot more dense. Plan on what livestock and corals you want to have, build scape to support them, and once you are done, that is how much rock you need.
If you're talking real live rock...then 1 is enough to cycle and seed your tank. If you're talking long time keeping fish/inverts happy looking good aquarium and lots of sites for corals...even more. Just remember if having fish too that the real swimmers will want free space to swim in and crabs and shrimp and gobies want all the rock possible to hide.