There's a thread here on APUG entitled "darkroom portraits," IIRC, that may give you some ideas about layout, blacking out windows, etc. It's a long thread and I don't claim to have read the whole thing, though.
Blacking out windows is certainly possible. You'll probably use a combination of a solid block of something (styrofoam, wood, whatever) and a black cloth or plastic sheet.
Water is more of an issue. You can develop film in a kitchen or bathroom, and just load the tank in the darkroom, so that's not a big deal. For making prints, though, running water is very helpful. As an interim setup, I used a sinkless darkroom, and I was constantly running prints from the developing trays in the darkroom out into my laundry room so I could put them in a print washer. Depending on the layout of the rest of your home, you might be able to get by with a similar arrangement, but my experience was that it was a hassle. You could also hold prints temporarily in a dishpan of water, but resin-coated (RC) papers delaminate after a while in water, so you'd probably want to hold prints there for just a few minutes to an hour or so. Using tanks of water might be an acceptable workaround.
Temperature control may not be as important as you think, especially for paper. There are developers that are formulated to work at high temperatures, so you may be able to use one of them, if necessary. You might be able to use a more conventional developer even at significantly above the usual optimal 20C temperature -- say, 30C or 35C. Temperature control is more important for film, since film development must be terminated before the process is chemically complete, and this time depends on the temperature. Cold or hot water baths do a good job of this.
An eBay search on "Durst M805" didn't turn up anything for me, and I'm unfamiliar with that specific model, so I can't comment on it specifically. Certainly very few used 35mm or MF enlargers would command that sort of price in the US, although some exotic LF enlargers might (I'm less familiar with that market). If US$900 is typical of enlarger prices in Hong Kong, it might be worth disregarding the advice that most people have given about buying locally. I don't know what it would cost to ship an enlarger from the US or Europe to Hong Kong, but I suspect it'd be well under that value, at least if you select slow ground/sea shipment. At the very least, it might be worth asking a few eBay sellers about shipping options.