Pry up the pebbles at the opening near the tree using a bottle opener (works for me) and once you get it started, you can just peel off the rest in chunks. Fill in the blanks where a lot of soil comes with the pebbles and do use warm water trickled around the edges to soften the glue, then scrape off with a butter knife. I also suggest repotting into a fast draining grit vs the (probable) peaty potting soil it's in (most 'potting' soil is mostly peat). Then you can water without being afraid of drowning it. Make sure you don't leave the pot in drain water, but put it up on large pebbles in a wide tray of water to humidity the foliage, and keep it in full sun throughout the day.

I can tell you from experience, you won't be able to affect much change. It seems that once they are whacked to the trunk right above the bulbous root, it doesn't really get any taller. I have had mine for a year and a half and it is the same size - no upward growth, just branches coming from the apex of the trunk. There are things you can do to get a bushier top and that is about all you can do. You might try to find a book on basic bonsai or bonsai for beginners. There are leaf pruning techniques that will cause it to branch out more on top. Good luck. What ever you do with your soil, you want a 50/50 mix between organic and inorganic. Your inorganic will be in the form of grit (decomposing granite, irregularly shaped pebbles, fired clay, etc.). You should use between a 2mm and 5mm sized grit and whatever organic you're going to use. If you root prune when you pot up, don't fertilize for about five or six weeks, then, fertilize with house plant fert. once every two weeks. Good luck.

From my understanding, some plants acquire these when the leafs stay too moist for too long in shady conditions like over crowding in big box garden centres where they cram larges trees in small over lapping spaces. If its not a huge issue with you, pluck the few affected leaves if there isn't many, and watch to see if its spreading. I would also wait and see if after fall when it loses its leaves if it returns next spring. Could just be a seasonal issue.

Not sure about first 2, but the 3rd is definitely a Peace lily (Spanthiphyllum). 4th is a Maranta leuconeura (Prayer plant). I'm not an expert, but there are my advices about how to look after them: They both like being away from direct sun, water them thoroughly with filtered water when top 2-3 cm of soil is dry. Make sure they are not sitting in water though. Also keep them away from heaters and cold draughts, spray the leaves with soft water when air humidity is low. Don't need much fertilising, half strength every second week will do.