Hey Marco. Those are some very well-built capacitors--0.75~ nF from a single bottle is excellent. It sounds like you could do fine with only 8 of them, in that case. You can keep the extras on-hand as backups
I'm afraid wiggling the bolts won't help. They have to be very clean in order to work. I hate to say it, but you might have to dump everything out, clean the bolts, put them in, and then put in the water and oil. Before you do, though, go ahead and test it the way it is now (minus 4 bottles). It might work anyway.
Now that the capacitors are done, I think it's probably about time to hook them up to the rest of the setup. I would use the configuration with the spark gap in parallel with the transformer and capacitor in series with the output. This helps protect the transformer in case of large voltage and current spikes.
I look forward to seeing your progress!
Best wishes,
Matt