1. If armies on target terr go up, it is transfer, if they go down, its an attack. Having different colored arrows would only add more information to the screen, making it even harder to see whats going on and where. On top of that, WZ already has plenty of colors, so it would only cause more confusion if arrows become multi colored.
2. There already is a bubble showing how much was deployed. Since 5 was deployed and the total is 10, you also know that it had 5 armies before the deployment.
3. If you just watch the turn, you will see every move 1 by 1 (thus you know the order). If you want to view it all at once, just look at the orders tap for the history, where each order is displayed in sequence.
4. The number of armies in an order is clearly displayed in a box in the middle of the arrow:
5. Same point as 1, would only cause more confusion. If you find purple hard to see, dont select purple as your color.
6. The arrows are indeed covering the numbers, but offsetting the tail too much from the center of the terr might cause the tail to be moved out of the terr when the terr is too small (<30 px big)
7. Having armies highlighted is troublesome because WZ then needs to figure out which armies you can still move. That effectively becomes a free AI, so thats not good. Highlight every territory with 0+ armies, is not a solution either, because most of the time you actually want those armies to stay where they are to defend or be useful in a later turn. On top of that, checking of you still have spare armies on the map is your own responsibility, and part of the skillset that makes you win or lose games.