My reason for using several enlargers is to avoid the pain of being adjusting with every change of lens... it could be great to have a multiformat enlarger, but in my experience it is unpractical. Some enlargers get out of alignment with a simply change in the head`s height... so I prefer to use at least two enlargers.
I work in two darkrooms, #1 with a condenser 35mm head and glassless carrier, and another dichroic 4x5" with glass carrier, #2 with a condenser 6x6 head with two carriers, glassless 35mm and glass 6x6, and a second enlarger, also condenser, with a 6x9 glass carrier.
Think that if you don`t plan to have big enlargements from 35mm film, the 35mm enlarger can be ruled out... in the other hand, if you don`t shoot medium format so often, 35mm enlargers are tiny and very comfortable to work with; in this case, a 4x5" enlarger could be the best companion. As mentioned, it will depend on the formats you use most.
If I were building a new darkroom, and money were not an issue, I`d have a condenser 35mm/6x6 enlarger and a dichroic 4x5" one... to my taste, the best ones are the Durst A300 for 35mm, Durst M805 up to 6x7, and Durst L1200 up to 4x5". If money is an issue, the best amongst the cheapest to my taste are the Meopta Opemus 6 condenser, and maybe a LPL 4550 dichroic. With most cheap (but good) enlargers you can get the very same results, but with a noticeable lower confort level.
About sinks, I like to use two sinks; a small (kitchen type) one for film developing and chemicals drainage, and a big second one for the trays and washing devices.
Big, flat sinks have a slow liquid drainage action, they never get completely clear and it easy to keep chemical remains on it. If chemicals were water and soap, no problem, but if you want to get rid of a selenium solution (or pyro, or whatever dangerous chemical), any trace of chemical could be dangerous for your health.
For this reason I like to have an small sink, with a good drainage action, where residues are easy to drag with water. Better if your trays fit in to be cleaned.
Plastic sinks are not so cool, usually on the small side, but functional and with the better drainage. Wood ones are cheap but take a lot of work (depending on how good you made it), steel ones are supercool, light and strong but usually with not so good drainage.
Just build a darkroom for yourself, or maybe for you plus an assistant; three persons on a darkroom working at a time is not so realistic (at least if you are doing serious work). Simply too much people (you`ll need two sinks, three enlargers, etc... Do you really need it?)
Just my 2 cents.
