Looking great! Add a nice black background, spray paint or replace that E-green inlet tubing, and you've got a winner!
Regarding your questions -
1) Either way works, if you have a little, it's better to split it up and spread evenly for fastest coverage. Looks like you have plenty, and with some patience you will have the same result without the need for planting one-by-one.
2) Give them some time to get established. Not every plant will grow in your tank... Be prepared to chuck some and replace with others. Nothing wrong with that.
3) Not sure... For me this plant does better in cold water. It is often sold for ponds. It should resprout from its nodes.
4) Couple of weeks... If you start with a very small amount, it will take a while to show a significant increase in substance. Patience is the key.
Really nice start.