#4 - I can help you out with these!
There are two types of STOCK turn signals.
One of them, which is the same ones I had on my XT stay on all 4 at all the time and also blink. These have Dual filament bulbs and three wires come out of it!
The other type has one filament bulbs and only two wires come out of them!
Which type were your stock turn signals?
If you have the 3wires ones you might've plugged in the wrong combination!
Still, you need a special LED flasher relay or they won't flash as they don't draw enough power from the flasher to trigger it and so, they always stay on!
Did you buy the correct taillight?
Those LED taillights have either two series of leds, one for presence and the other for the brake lights or another way that right now I can't remember... OR they actually only work as brake lights.
The thing is, you should also have 3 wires coming out of that taillight.
Any less than that and you'll only have either brake or presence light!
If there are three wires you need to check that positive third cable as it is either broken somewhere before the tailight OR actually Inside the taillight!
METHOD: change the wires to check if it's the taillight!
You got two options!
Option #1: Plug the wiring loom presence light POS onto the taillight brake light POS.
Does it light up?
Option #2: Plug the wiring loom brake light POS on to the taillight presence light POS.
Does it light up?
#2 - Guess you've answered it yourself! =P
#1 - I think your problem here is a faulty neutral switch!
There should be a small cable which is routed very close to the countershaft sprocket that connects to the neutral switch.
The top of the neutral switch resembles to a sparkplug...
I had something like this on my XT...that small cable was heavily corroded and a cleanup with some sand paper worked!
That's about it...