You've raised a few issues in your posts, so having just built a new house I'll address those I'm able to:
To start with, I live in a country/area where corrugated steel roofing is the absolute norm and has been for over half a century. In my town less than 1% of roofs are clad in anything else. Everyone collects rainwater. Everyone uses that rainwater. Most people drink that rainwater. There are no health issues associated with properly built and serviced rainwater harvesting systems.
The most common rainwater tank material around here has historically been zincalume (combination of zinc and aluminium). So drinking water has been stored for years in containers significantly made of aluminium. Once again, no negative health effects.
Brand new zincalume tanks do leach zinc into the water intially, and this is what gives water held in those tanks its 'metallic' taste. But zinc is actually a mineral that humans need, so (apart from the taste) that's not a problem. Every season the amount of leached zinc decreases. Whilst the impact on taste is quite noticeable in the first year, you can barely taste it after about five years.
Aluminium does not leach into water like zinc does. The amount of aluminium that will end up in your water if you have aluminium roof sheeting, gutters, downpipes, or tanks is negligible providing the aluminium is not subject to mechanical abrasion. The most likely cause of abrasion is the impact of falling branches.
If you live in an area surrounded by trees, and the wind blows small branches onto your roof on a regular basis, then that's a problem. The kinetic energy of a falling branch is sufficient to break through the aluminium oxide layer upon impact and gouge out a small amount of the soft metal. These tiny specs invariably make their way into your water tank and ultimately into you. If you're always clearing twigs/sticks out of your gutters, I'd either clear away the trees causing the problem or go with (hard) steel roof cladding instead of (soft) aluminium roof cladding.
Price is also an issue. Local economics have a huge influence on the (relative) price of different types of metals, and here aluminium roof sheeting is 3x as expensive as steel. In other areas both are about the same. YMMV.
I don't know why you say that corrugated roof sheeting is "impossible/difficult to walk on". I've never had a problem and I've spent countless hours up on corrugated roofs over the last 40 years or so. If that view is gathered from third-parties, I'd advise not paying them much more attention. Continuous corrugations make for a uniform surface that is much less prone to tripping than the type of surface depicted in the image in your second post.
On the subject of profiles, the profile of that Fabral panel has large amounts of flat surface. Flat surfaces tend to accumulate clumps of debris (e.g. dust/dirt/pollen/leaves) because water always takes the path of least resistance and tends to flow around obstructions rather than trying to push through them. Thus if your area has long periods of no rainfall, debris will build up and the first (usually light) rains will not wash off the debris. The intensity/duration of the rainfall needs to increase before flat surface debris is dislodged — and by that time your first flush diverter is already full and the clumps of debris go straight into your tank > tap > you.
Corrugated profiles are half valley, half ridge. Debris naturally ends up in the valleys and, because that's where all the water is forced to go, is pushed downstream immediately — even in light rains. Corrugated profiles are thus the best profile to have if you want to have a 'self-cleaning' roof.
Corrugated profiles complement first-flush diverters. Flat profiles undermine first-flush diverters.
Moving on, we have the issue of gutters. Steel gutters rust out (and begin leaking) in as little as seven years around here. They are terrible. That's partly due to the material, but mainly to do with how downpipes are connected to the gutters. Local tradesman cut a hole in the gutter, pop in an insert, rivet it in place and put a bead of silicone around it. The downpipe is then friction-fit (or riveted) to the part of the pop that extends below/outside the gutter. The pop/silicone creates a ridge inside the gutter that allows water to pool and debris to collect, which fosters microbial activity, turns the water acidic and rusts out the gutter.
Going with aluminium or plastic gutters is a good idea as it mitigates what would otherwise typically be the first point of failure in your average roof-based rainwater harvesting system. (Note, however, that plastic may not be allowed, and isn't a good idea, if your house is located in a bushfire-prone region.)
The same 'self-cleaning' logic that applies to roof cladding applies to gutters as well. A gutter with a square profile (flat bottom with sharp corners) will accumulate debris and undermine your first-flush diverter. A 'half-round' gutter focuses everything to the bottom, self-cleans, and complements your first-flush diverter.
A small detail that most people don't pay much attention to is the type of bracket used to connect the gutter to the fascia. It is — unfortunately — normal around here to 'hide the brackets' by using a type that fits inside the gutter. Such internal brackets may make the gutter look more streamlined, but they block the gutter and force you to either climb up on a ladder a few times a year to clean the gutters out by hand, or precariously walk/crawl along the edge of your roof with a brush/scoop. Both are dangerous and/or dirty jobs.
External brackets hold the gutter in place from the outside. They do not obstruct the gutter. That means you can attach a brush to the end of a pole and (assuming you have a single-storey house) sweep clean your gutters from ground level. As far as I'm concerned, that's pure awesome.
My house has corrugated steel roofing and half-round aluminium gutters with external brackets because that combination was the most self-cleaning I could come up with. I clean my gutters from ground level. Apart from having to maintain the wood heater chimney/cowl, I have no need to go up on the roof. Rainwater quality is excellent and I will be long dead before either my roof or gutters fail and need to be replaced.
Sorry about the length of this response. Hopefully there's something of value in amongst it all for you to ponder.
