Tube Forming and Wall Thickness

Talk to your local hose/tube/fitting distributor to have one made for you.

Do you think we are talking about conduit RV? For bending conduit there is a simple tool. PVC pipe comes in straight, 45, and 90 degree segments that are simply glued together.

we're talking seamless carbon steel. Don't think I ever saw a push flare or a double bubble flare on conduit or PVC

Is it a critical application? Because there are some limitations if it is...

The bends are hard to tell with a plain carbon steel if they re going to be as tight as you wish. Keep in mind that it's always a good thing to assume that the bend will have the same radius as the tube is (in a minimum), and some wrinckles and shrinkage may occur, specially if you don't use special tools. If its not a problem, you could also use the old indian trick of filling the tube with sand and use a curved surface to bend the tube on (with the desired bending radius) helping to avoid tube collapse at the end it is compresses - in the inside of the bend. If the bend is close to tube ends, start with a longer tube, bend, and cut the ends at desired lenght.

For the flare and expansions, better use flaring tools. If not requiring to be leak tight for some connection or precise, then maybe manufacturing a punch from a little harder steel with conical end may solve the problem.

But maybe some of the other guys here can have a better suggestion. This is my personal experience, and it may not be so good as some guys here that work with it.