New Set Up.

Hi there all, I am looking at converting my existing tropical
freshwater Trigon 350 (litre) into a marine set up, although initially
without any corals - I would like to progress to a reef setup at some
point in the future. I intend to start the system using the internal
Juwel filter and an external Fluval 203 feeding an undergravel plate
(in reverse mode) covering about 40% of the base of the tank. I have a
few question which I would like answering in respect of this, these
are as follows :

1. Would a skimmer be required in a tank of this size or is that more
dependant on stocking levels ? If so, will a Aqua-Medic Miniflotor
Skimmer be man enough - quoted for use upto a 200 litre tank !!

2. Do I need a steriliser ?

3 Would a sump setup be a better option right from the word go ?

4. Are they any downfalls or issues in using this type of setup /
filtration that I should be aware of ?

Many thanks in advance to all who may respond.

Kind regards,

Steve.