The main pendant is from a pair of old earrings, which were too heavy for my ears. Some of these beads are from old broken bracelets etc; I like re-using things like that :)
Just use headpins, eyepins or simply wire to make loops either side of the beads and attach them together with pliers.
Make the design so it is asymmetrical, more one side than the other of the main focal pendant. Attach the chain onto the end of your linked beads once you're happy with the position.
To make things easier, make your necklace long enough to go over your head without needing a clasp!