right first start by running the co2 hose down theback of the tank (much easyer with nothing atached to it.) get some little suckers to hold the pipe in the top of the tank, or wedge it some where, secure..
then you should wind some PTFE tape around the thread on the bottle, keep the tape wide you don`t need much only need to go round 2 or 3 times make sure you can see the thread under the tape.
i cant quite see how your solenoid attaches to your regulator, so closer pics of the reg and solenoid would be helpfull.
once the solenoid is atached t the reg tighten the reg onto the bottle, and ajustable spanner is what you need make sure its on tight.
now atach your co2 hose to your solenoid, (its usualy a simple push fit)
With the type of diffuser you have there i wouldnt bother with the bubble counter as you can count the bubbles in the diffuser.
so simply fix your diffuser in your tank and turn everything on.
once you`ve tinkerd with the various valves untill you get the bubble rate you want, get brust and some wahing up liquid in some water and apply it to all the joints that are out of the water if you see bubbles forming you have a leak,
if you discover a leak on a threaded connection add more ptfe and tighten it up.
if its on a push fit connection i found wraping it in lots of ptfe works well.....
hope that helps.