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I'm
trying to do a natural tank, currently with low light basic
fluorescent. I want to add some high light requiring plants and use
natural sunlight for a few hours, probably in the morning. Is there a
'right' amount of natural sunlight. A proper amount of time and portion
of the tank to receive light? What other considerations and temperature
controls should I consider?

I'd be very careful trying to
use direct sunlight. It's far more intense than any artificial light,
and like you hinted at, can cause temperature issues as well as algae
issues. Diana Walstad's "el Natural" style of fishkeeping
advises placing the tank near a southern-facing window so it gets a few
hours of sunlight. This means it won't really get blasted by the sun at
any point during the day directly. I don't know the exact details, but
I don't think that this would be enough for a high light plant to grow
well in. You also have to consider the angle at which the light is
entering the aquarium. You're going to get most of your plants growing
sideways towards the sunlight. As for temperature, the sunlight will
heat your tank quite a bit, especially in the summer, so you may need
to use a fan or chiller to keep the tank cool. Also, since it's likely
going to be next to a window, keeping the tank heated in the winter
will be more expensive and require a better heater. Sunlight also tends
to encourage algae, so you'll have to work a little bit harder to keep
that in check. Overall, I'd say using natural sunlight isn't a bad idea
if you want an "el Natural" style tank with low light, low maintenance
plants. However, I don't think high light plants will thrive under
these conditions. They need constant and direct high intensity light to
really grow well.

Any tips on making DIY caves? I'm going to make some for my fish soon - preferably from natural materials. Any suggestions?

Well the most natural caves would be crevaces made by piles of rocks. Just make sure to select rocks appropriate for the aquarium
and start building. If you're looking for a cave for breeding purposes,
although not the most natural, halved coconuts and upside-down flower
pots with a hole for entrance are the easiest ways to go.

Ask
a question about aquascaping, keeping aquatic plants, plant-friendly
fish, lighting, CO2, fertilizing, or any other aquarium plant related
question in the comments to this post, and I'll answer them in next
week's edition.

Source: Aquatic-Eden.com