yup once you got a pair you'll get aggression towards the others. you'll need to get the pair into their own tank. add a little aquarium salt and acriflavin too if you can find it it'll help the healing
think you meant "aren't" cheap fishplants. yup as above and add in that they like warmer water (27-29c) which hits the power bill more too. and good quality food.. but go for it! they definitely rule and are fun to breed
how'd they go?? i know this post is old but if it had something that looked like food on it possibly it's fungus. and yes it gets easier usually it's plain-sailing but things do arise from time to time
it's perfect. all those fish prefer a low pH like yours. and the hardness works like a buffer; the higher it is the more stable your pH will be. it's not 0 or 1 so it will hold fairly constant. baking soda will bring it up but you don't need to add it. worst case scenario if you were running CO2 and had it heavily stocked the pH potentially could crash