Hey Lady, welcome to MFK, and glad to hear you are getting back into the saltie world!!
First off, sit down and get comfortable, this might take a minute.
Ok so when it comes to rocks, I don't know where you got that ratio either (of 1 lb. of rock per 10 gal. of water), lol. Mmm - No. Most often, and especially when relying on the live rock to be your main source of filtration, you are going to want to balance your rock more proportionately with figures more along 8-12 pounds of rock per 1 gallon of water. However, weight isn't always the most important thing with rock, as sometimes you can have massive pieces that are less dense than smaller ones. This usually is going to vary depending on their origin.
The most important factor with live rock is surface space, as we all know that what makes this rock living, is the micro/macro-organisms, algae, plants, and bacteria which take up residence within its porous structures, and therefore, naturally, the more rock you have the more filtering and detritus eating animals are able to be supported.
Overall pounds are used because that is how they are calculated for retail cost, and for the most part, are pretty accurate when it comes to size, however I have a large table-top piece of rock that weighs 1.5 lbs less than a much smaller grapefruit sized rock. Soo, look not only for the weight but also for how much rock you are actually getting for that.
When it comes to the filters, there are several types of media which will forever produce varying opinions, however, they can all work well if you know how to maximize their potential and you are an active maintenance person, keeping a regular and strict schedule. Some of the better options for those who don't have the time or give-a-crap to spend a lot of time on the cleaning, is sumps and canisters as they are extremely versatile, when it comes to customization for different tank needs, take on the bulk of the filtering, and do not require as much (though still regular) cleaning.
Bio balls are great but like mentioned, they can sky rocket some of the more dangerous parameters if not kept in check. An alternative to the plastic balls, bio bale, etc. would be as mentioned, live rock rubble, which you can throw in some base rubble with it too which will seed quickly.
As far as what you intend to keep in your new tank, there are only a few eels which would fare well in a 55 and I'm sorry, but no sharks would be suitable for that size, it is simply far too small.
Additionally, figuring out the stock can wait, seeing as you just started the cycle, so in the mean time, focus on your filters and your cycle and make sure that everything is balancing, and then we can get into the stock-choosing. When it comes to mixing your water in advance, unless it was in a sealed container, I wouldn't suggest keeping it too long as you will be exposing it to insects, their eggs, bacteria, mold/mildew spores, and algae.
When you purchase seawater from retail stores, their water has been finely filtered and sealed, so it's shelf life is significantly longer. However, if you were interested in pre-mixing water to allow for dechlorination, then you would be fine keeping it for a few days in a garbage can like that with air stones, and turning the water a few times a day. But really you only need to allow a minimum of 24 hours for that, so making more than you were going to use that week probably would not be the best route to go since you do not have a system for holding water at this point.
All in all though I think once you start researching and brushing up on the old and the new, then you will have a great experience again, but yea.. No sharks in that tank ok.

Let us know if you have any more questions.
-Em