How can I make or what should I use to get good 90º angles to connect the push-rods to the servo arm.

Not sure what you are talking about. I make all my pushrods with dubro solder-on clevis's on one end and heavy duty metal clevis's with spring retainers on the other end. Safe, reliable and they come out perfect every time. If you are using quick locks or something similar, you could use a panavise and a hammer. I have a friend who uses that method and it works well for him.

I just use my lineman's pliers. A vice-grip will do well too. I've been doing this lately...one 90 degree bend into the servo arm and the smallest wheel collar the rod can use to lock it on.

I usually clamp the rod in a vice and take a small tack hammer, hammering lightly until the bend is 90*. Works well.

If you use ONLY a 90-degree bend instead of a z-bend, you should have something to retain it in the servo arm. Squareloop mentioned wheel collars. Someone (Great Planes??) makes this little plastic whatzit that snaps on to the rod and on the rod above and below the servo arm to retain it. I've used them before with no problem.

Get your self a Z bending tool from your favorite model shop. It will make the job nice and easy. They are a sort of pliers which bends the wire into the right shape you want to connect it to the servo arm.

Nick