Hi Mark....and welcome to Wetpixel !!
Two months in Malaysia !!! Lucky you !
I figured some of the more knowledgable folks would reply to your question, but since they haven't I'll try to help with my comparatively limited experience.
You have a good camera for underwater use. There are better lenses out there of course, but I have seen some excellent UW pictures taken with the 18-55.
There is a seemingly endless selection of lenses and ports available and it gets confusing trying to decide what would work best. If your budget allows, I would recommend the 60mm macro lens. It will work behind the same flat port as your 18-55. The zoom lenses seem to work better behind dome ports, but if your budget is limited to one port, you can use both these lenses with the 5502.
You will want to use the 4103.51 sync cord. The slave sensor can be used with this housing and camera, but it is triggered from a second strobe and you indicated you would only have one.
As far as spare parts, perhaps a spare housing o-ring and strobe o-ring. If you plan on doing night dives, the DS125 has a good modeling light built in and a spare bulb for that might come in handy as they do burn out. Follow the Ikelite recommendations for maintenance of the housing and o-rings. Pretty simple actually, just rinse everything well in fresh water and make sure the o-rings are sealed and clean.
Hope this helps.
