@a_ibrahem Hi buddy.
Apologies for the late reply! Awesome work you done there buddy! Should be really proud of your work! I too have used plastic fittings 90 elbows and T bends. I more than fit for purpose for the job, so no need to worry there. But if you are worried I believe you can get those 19mm I.D fittings in brass.
With the mount for the catch can it was just abit of straight aluminium plate about 30-35mm wide and 4mm thick that I painted black to make it look more OEM. I then M6 threaded the plate so that the two bolts would screw on it plate in to position and even added nuts underneath to make it more secure to the frame of the car.
With the bolts for the catch can I just drill two holes through the plate and use the fixing bolts supplied with the kit to attach the can. Hope this helps.
From the first image I have posted I have made some alterations with the pipe work fittings will get a picture up asap for you to see