At least you figured out how to get the thing assembled. Good work there. As far as the sear release, I'm having to think on that one a little.
A few things come to mind.
Trigger blade screws: (You don't need to disassemble the rifle to perform this step). You installed new trigger blade screws. They need to be set inward far enough (CW) to hit the trigger rocker-sear correctly or the rifle simply won't fire. The front screw on that trigger blade adjusts the first stage take-up, the rear screw adjusts the second stage let-off. Let's do this safely! With the safety reset, using one finger of one hand to support the rear of the trigger blade so it can't move and cause the gun to fire, try turning the rear screw 1/4 turn inward (CW), then release the safety and try to fire the rifle again. If that didn't cause the rifle to fire, try another quarter turn, etc. Keep track of how many turns you turned the screw so you can put the screw back where it was if that doesn't fix your problem or give you results you like. BTW, I noticed you have two non-OEM screws in the blade. Is that rear screw long enough to actually hit the rocker-sear soon enough? If not, you might need to try a slightly longer screw. In any case, once you get the rifle to fire, you can slowly add some CW turns of the front screw to give you a nice first stage and a crisp second stage, but still with no trigger creep. If you don't get a second stage at all, the first stage screw is turned in too far. Back it out a little and retest until it works right. I tend to think this item is what's actually going to fix your problem.
However, if that fails you may in fact want to disassemble the rifle and re-check the way you have the internal parts of the trigger assembled.
Trigger plates: The way it always made the most sense to me from a functional standpoint regarding the installation of those two flat plates is to have the rounded end of the front plate facing forward (towards the muzzle), and the rounded end of the rear plate facing rearward (towards the safety button). In other words, the two flat, non-beveled sides of the plates would face and rub against each other. However, I never saw an instance where installing them another way caused a failure of a sear to release the piston. In fact, sometimes when I got a rifle with a T05 trigger directly from the factory to tune, the plates would be facing the 'wrong' direction and the rifle would still cock and fire OK. The next new one I got would have the plates facing a different direction and that worked OK too. I'm not saying that facing them in the wrong direction isn't the cause of your problem, I'm just saying I never saw it here. I don't think it's your problem, although I prefer to have the plates installed the way I told you.
Still not working? This may help: You can test for proper operation of the trigger/sear release and the safety while the trigger assembly and the piston are out of the rifle, with the spring totally out of the picture. You'll need to install the two pins into the trigger housing so the parts stay where they belong while you do your testing. Push the rod on the piston straight back into the trigger housing until you feel a very-light 'click' telling you it's in the cocked position (if you don't feel or hear the click, try pulling the piston out of the trigger housing--if it won't come out, yes, it's cocked). Then release the safety, pull the piston straight forward towards you from the housing, and pull the trigger blade. You may need to pull on the piston fairly hard to duplicate the pressure the spring applies when it's cocked. With you pulling on the piston while you pull the trigger blade, the piston should come out of the trigger housing to simulate a 'fire'. If the piston won't come out of the trigger housing during this test, it's not going to work when the parts are installed in the rifle, either. You'll have to figure out what's wrong before you reassemble the rifle.
You didn't install a new mainspring, did you? Having too many coils on a spring might allow the rifle to cock but put it into a bind. That might cause the safety to appear it's in the 'Fire' position when it's pushed forward, when that's not really the case. If the spring is the right length, did you perhaps install any spacers into the piston or onto the rear spring guide? If so, you might need to remove one or more spacers and reassemble the rifle. If you're still using the same spring and guide set-up as you got from the factory (or that worked OK when you you were previously shooting the rifle), and you added no spacers, this item doesn't apply to you.
This is kinda straining my brain and I can't think of anything else to tell you at this point. If I was there I could probably figure it out pretty quickly, but it looks like you're mostly on your own.
Safe and Happy Shooting!
Ed Krzynowek, The Airgun Tune-Meister
"We can rebuild the squirrel. Make him stronger, faster...We have the technology"---Skyler M.