No. The client will be able only for older versions before "1.9 PvP" based versions, because it makes some client functions unnecesary. Like CPS (Clicks per second) functions or "1.8 -> 1.7" animations.
Not for now. Because we are trying to find methods for do that into the future. For now, you can use our default in-game cosmetics for Free.
Try using other Internet connections. This may help, because there are many local networks that blocks downloads of many files, like JARs & JSONs.
First, thats a false positive from antiviruses like Windows Defender, detected as "wacatac.b!ml". It says that executes commands from attackers, but it isn't do that from us. For more information about how to disable it, please enter to this link and do the steps from the last web section.