I think if your just beggining then you should have 1 tank to dedicate yourself to. This way any problems can be tooken care of without worry of another tank. I prefer multiple but since I dont want to have problems I am sticking with 2x 10g's. And they are both low maitnence due to low light. But obviously it depends on weather you have a low tech/low maitnence tank or a high tech/high maitnence tank and how experienced you are.
Multiple tanks. Sometimes it comes in handy to swap plants/fish around. Especially if doing a restart. It can sure be a time hog, but its definately cool to look around a room and see three or four planted tanks with the lights on..
I have 12 tanks right now. I just got a job to maintain 150 more tanks at a LFS. I think I will cut down to maybe 3 here soon. I will always have MTS and probably collectoritis. MY rooms Glow Green at night. It is a sight to behold. Just ask guitardude about my last place.
I have one main tank(which for now is my 20g tall show tank) that houses a little bit of everything. Then I have a couple smaller tanks that house species only in each(shrimp only, neon tetras only, etc). I've DEFINATELY got mts...i just got my shrimp tank up(not even fully cycled yet) and I'm already looking for another tank!
I'd like one really large tank(like a 180 or a 240). I'm dreaming of Pseudoacanthicus and Panaque.
However, with smaller tanks, like my two 60-P's, even *I* can pull off a decent aquascape, and it is easier to do maintenance. I can also keep different varieties of inverts that require their own tank or are incompatible with other species.
You meet some knowledgable friends or crash course family members to just do "basic" tank duties while you are gone. That takes a lot of trust to pull that one off though. You can read the horror stories of vacation tank mishaps here on TPT and other sites. Also, you can temporarily make those "high-tech" tanks into "low-tech" tanks while you vacation, most do ok.
I think it's more difficult to have just one tank than multiple tanks. There are so many different critters and plants species out there that you just got to have. The real hard part is choosing what to keep! LOL
I also have developed MTS. The first tank was a 2.5g goldfish tank that killed several goldfish due to my inexperience and the small size combined with the heavy bioload of the aformentioned fish. (oh yey the 2.5g tank was the girlfriends idea (not mine)) Since then I have bought a 20g and a 75g (not the girlfriends idea). So her need to have a 2.5g tank has turned me into a fishtankaholic. I don't think I need therapy yet.