David Attenborough.

I win.

It isn't worth the risk. End of story.

There's very little work done in a fishless cycle- a couple of water tests each day, a big water-change at the end of the process, and perhaps a couple of mid-sized changes in the middle if you have soft water and your cycle stalls. Fish-in cycles, as noted, involve doing a water-change nearly every day for anything up to two months or more.

It might seem like a long time to wait, but it does allow you to spend time aquascaping to your liking, getting any plants off to a head start, and working out what your stocking will be.

Follow the instructions for the fishless cycle and you'll be fine. Liquid ammonia is the easiest method, as you know exactly how much you need to add to top up as the cycle progresses. Do not add fish until your nitrites and ammonia both read zero 12-24 hours after adding a dose of liquid ammonia. Mine took about 5 weeks. Two months is unusual, but not unheard of. If your water is very soft you may find your cycle crashes. This is usually caused by a drop in the quantity of carbonate in your water (KH), (the bacteria that "eat" your nitrite and ammonia use carbonates as part of this metabolic pathway) and a good proxy is high nitrates in the middle of the cycle rather than at the end.

While you're waiting for the cycle to run its course you'll have plenty of time to research the fish you want to keep, get your plants going, etc.

Cleaning the filter media should always be done in old tank water. How regular this should be will depend on how much gunge your tank accumulates- I've not bothered cleaning the external on my 60L in several months, but I tend to do the external on the 240L once a month or so.

The glass should be cleaned as and when necessary. I do the outside whenever I do a water change (I always end up spilling a little, and I don't want to look at watermarks- my water is very hard so I get lots of limescale). I give the front and side glass a go over with a algae magnet or razorblade on a stick as and when necessary (ideally just before a water change so any large bits of algae dislodged can be sucked up).

Gravel vaccuming is usually done whenever you do a waterchange. This is a good article explaining how to do it. Dig around in the gravel while removing your water, and you'll remove any grot that's collected in the spaces between your substrate grains. This doesn't work with sand, (you'll suck it all out and dump it in the bucket) but you tend to find dirt accumulates on the top so its easy to remove by swirling your siphon tube around.

After you've removed about 20% of your water replace it with fresh water that's been dechlorinated and brought up to temperature. If the water out of your tap and in your tank have notably different pHs then you should age the water for 24 hours or so before doing the water change.

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White Cloud Mountain Minnows and Rhinogobius wui. Who needs a heater. ;)

Danios, being one of the model organisms, if they want to do tests to check toxicity to aquatic organisms, I'd have thought they'd have done it on them. Whether they've bothered to do the tests- especially on larval ones- is another matter entirely.

I wouldn't worry about marbles, and just get some marble-sized pebbles. I doubt you'd spend more than a couple of pounds on enough to line the bottom of a 24" x 12" tank, which is all you need for spawning. Just put the conditioned adults in, watch to make sure they've mated, return them to the main tank, and watch for babies.

A 25L tank can support no goldfish. Adult goldfish need tanks of at least 150L or so for the first fish, and an additional 50-60L for each additional fish.

Personally I don't think there are any fish suitable for 25L tanks. FK recommends a minimum tank size of 45L for Bettas, and 60L for small shoaling fish. There are some very tiny fish often sold for these nano tanks (microrasboras, ember tetras, etc, which don't get above 3cm) but tiny tanks give you much less margin for error than larger tanks, and I've always been of the opinion that bigger shoals look better, and these very small fish are often timid unless they have large numbers, which you can't accomodate in a 25L.

Shrimp however would be doable. You'll need a heater (25W will be fine), to keep the temperature stable (small tanks are susceptible to temperature swings as small volumes lose and gain heat much more rapidly) but Red Cherry Shrimp would be ideal to start with. You'll need to cycle the tank first- there's an article on the site about how to fishlessly cycle- you'll need a bottle of ammonia or Waterlife's Biomature, a testing kit (the liquid kits are the most accurate- strips are a waste of time), and a pipette for dosing.

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I'd have a heater on anything under 30L- cherries are pretty robust and as long as it stays above 20-22 degrees most of the time, and you don't have any sudden temperature swings they'll be fine. In big tanks this is not usually a problem, but small ones lose and gain heat rapidly, so a heater to keep the chill off is a good idea. Set it relatively low, and you should be OK. Be prepared to fiddle with the settings for a few days before you get your shrimp so you know it won't get too warm.

The Edge is pretty good from what I hear. The Chi is less so- Viriconia has one and lost shrimp because they climbed out, and got sucked into the filter (the light isn't great either). I suspect the Ebi and the Flora may have similar issues. The AquaOne AquaNano series look much better from that point of view, as do the Arcadia Arc Tanks.

If you buy everything separately you'll probably be able to get what you want, but it won't cost you much less than the all-inclusive kits.

Tetra, Interpet, and Nutrafin also make them, and they all come in at about £30 for the ones that do pH, Ammonia, Nitritre and Nitrate. There are kits that do other sests, but as you're not doing anything complex with fertilisers, you don't need to know what your phosphates, iron, etc is doing, and because your water is (probably) fairly hard, you're unlikely to get pH crashes which can stall your filter, and you're not attempting to adjust pH and hardness, you won't need to keep an eye on GH and KH either.

You can usually find what they are on your water board's website.

Lava rock will be fine, but to be honest its probably cheaper to buy the rocks and the moss separately and make your own. If you can see, measure, and handle the rocks you'll get a better feel for whether they'll fit with the aquascape you're planning.

Don't get the test strips, they're not terribly accurate. Liquid kits are much more accurate, and last much longer. I wouldn't bother cycling the Edge's filter- just take the media out of the spare filter and squidge it into the Edge instead of what you have there, or move the Edge's media into the spare filter and leave it there for a week or so and the bacteria will start to colonise it. You won't need many bacteria to cope with a few shrimp, as they have a tiny bioload, but the you really don't want to add shrimp to a half-cycled tank.