Help with worldbuilding

I have ordered Stephen Gillet's book on Worldbuilding from a vendor
listed on Amazon.co.uk because I thought that would be quicker. Alas,
they led me by the nose for six weeks before it turned out that they
never sent it and now I may have to wait another month before I get it
from the States (and then I still have to <i>read</i> the thing). All
this is getting to be a bad excuse for further delaying work on my
current novella/novel, so I hope you can help me out with some possible
flaws in the meantime:

The star should be orange and slightly cooler than Sol. I picked
epsilon Eridani at 0.85 solar masses as an example, with my world
circling at 0.4 AU, about 0.5 Terra years orbit (with help from
http://www.cix.co.uk/~morven/worldkit/index.html ).

The planet is a low gravity world, about 1/4 Terra's, half its size but
with a similar magnetic field and a breathable, <i>much</i> denser,
atmosphere (gliding plays a part in the story). It is largely blanketed
by clouds (if prevailing wind-patterns allow) and hence imaginatively
named 'Cloud'. Large parts of its non-polar landmasses (what proportion
of it has to be land?) are covered by dense jungle. It is very poor in
radioisotopes and has no discernable seasons (which I figure depend on
tilt). The dominant colour of the vegetation in the dimmer light might
be red/purple.

I have a biology background, but I'm less clever than most. However,
this is a story about ecology. The world is cooler than tropical Terra
and while the jungle (with massive trees, any idea how high they'd
grow?) is lush, it lacks the verocity of life in a tropical rainforest.
This is because the pace of evolution is glacially slow (low mutation
rate, apparently stable climatic conditions, low metabolic rates). The
two ecologists in my crew are wondering about this. It turns out that
every couple of 100 standard years or so, an outside event (comet?
Another star coming close?) triggers a complete turnover. What our crew
have arrived in is essentially the ecosystem in a state of hibernation.
Once they are happily settled and have defrosted their cargo of human
embryos, things start to happen, of course.

I would be grateful for any advise. I find this world-building lark
vaguely scary :}

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