I've been trying to fatten my male up with regular BBS feedings. Unfortunately he's not gained any significant weight, but she is now Faaaaat! He spends all his time fighting with his own reflection, whilst she piles on the micrograms...
Yep, that is just part of the process - nothing to worry about at this stage. Your set-up sounds fine - the only thing you have to be mindful of is not restricting waterflow to the return pumps which can lead to cavitation and bubbles - in your case that means not letting the black sponge block (I've got rid of mine altogether).
I'm a little suspicious of some of those pictures - the seller seemed a littlw unsure of whether the Mandarin was male or female, so probably not the best one to be bidding on anyway.
That isn't the way to do it. Tea introduces tanins (generally but not always good) and changes pH in ways you can't predict. A better way is to use bogwood, soft water, and do lots of water changes.
I don't think any oxidizable metal in a tank is a good idea, but I'd be suprised if it only killed the Rams and not other fish too. I'd chalk it up to line (in) breeding and weak genetics.
Speaking as an non-FNZAS and non-club member I would suggest doing lots of social things that bear only a loose connection with fish keeping. Why should fish club be only about fish? Have a JAWS DVD night. Go and see some wierd arthouse movie. Go to a cafe for coffee and a chat. Go to the Rugby (of course if you live outside of Canterbury your team will probably lose, so maybe that's not such a flash idea). Drink beer. Have a wine tasting night. All the fish-speak will flow readily enough anyway because its a common interest and when it doesn't you'll still be able to socialise. Basically do things that you could take your non-fish obsessed partner to.
You could try my secret magic recipe for breeding plecs - chuck the adults and fry into a planted community tank and watch them go for it. I suspect most catfish fry do well on a diet of random munge from under logs etc.
Warning: This may make you unpopular with people who think such matters should be taken more seriously.