hi, Converting a juwel does cost quite a lot of money. IMO i think you should not buy the juwel 400 and by a ready made marine setup, this is because these setups already have sumps, pumps, protein skimmers and the correct lighting whereas the juwel lighting is rubbish for marine (well for reef), you will need a protein skimmer, and if you are panning reef then you will need at least twin 150-250 halides maybe more depending on what you would like.
I converted a juwelk rekord 60 and it has cost me so much i could have got a setup double the size with all equipment for the same price.
With a tank your size, you will need at least 60kgs live rock, £10 a kilo is 600. RO water is a necessity.
JUst some things to think about.
Will