new tank questions: biofilter, sand cleaning, guppy control

Hi,

i'm still in the planning stages of a 500 liter/139 gallon tank and i
have a few questions. Recently, i asked the LFS for an estimate and
on that estimate i saw that there was no "real" filter. Just a built
in biofilter with some carbon and sponge. Maybe they missed on the
estimate and forgot to add a pump otherwise this doesn't seem like
a good system?
Tomorrow i'll be going back to talk to the people over there to
see if it was an error or not but otherwise, if this really is the
filtration system, i would add an extra filter, for instance an
eheim or something similar. Would this be overkill?

I'm also planning to use sand and quite heavily plant the tank.
Right now i have a small 15 gal tank and it's easy to clean the
gravel by using such a vacuum cilinder. ( or how is such a cilinder
with attached tube called?)
I don't think this is going to work in a bigger tank and having
many plants will also hinder vacuuming the gravel. This bothers me
a bit since on my small tank, the gravel seems to be really filthy
if i don't vacuum a particular part after a couple of weeks.
Then when i vacuum it, the water really smells which is not the case
if it's from an area that i vacuum regularly. But the water quality
remains very good so i suppose it doesn't really hurt either.
( unless you suck the tube too hard and swallow a gulp of fish
poo water )
Any tips/advice other that frequent waterchanges for a tank of that
size? Any links?

When i start the new tank i'm cleaning out my 2 small tanks and i'm
going to take the water from both to fill the big tank. This should
already cut down on the time it will take to cycle. I'm going to go
for the fishless cycle also.
Anyway, this is what is going into tank in the long run. I'm
planning to add them in small batches over several weeks/months.

7 x Corydoras Paleatus
7 x Corydoras Panda
20 x Cardinal Tetra
1 x Peckoltia Vittata
5 x Otocinclus
5 x Botia Striata
8 x Fiveband barbs
4 x Platies
8 x Guppies
1 x Betta
10 x Zebra Danio
2 x Dwarf Gourami

I added the gouramis as "pest" control for the guppy & platy fry
since one guppy infested tank is enough. I like them but they breed
to much. I'm not sure if i would add they otherwise but the misses
made a clear statement about them. Ouch, that was one fight i had
to back down from
So i hope that the other fish are going to be eating enough
fry to keep them from overrunning the tank.
Any other pest-control fish that would fit well with the current
batch?

flupke