I was just in western Fujian province a couple of weeks ago and visited a lot of those tulou buildings (still in China, so I don’t have pics up yet.)
My advice is that if you want to see them, see them now. When I went, I hired this motorcycle driver/guide and he was telling me in barely comprehensible Mandarin about the development that’s been going on in the area. Starting from about last year, a lot of the tulou’s have been charging ridiculous entrance fees - somewhere around Y50 for two or three - and it’s just going to get worse. Considering that in a day trip you’ll see close to a dozen tulou’s, those entrance fees can add up really quickly.
Also, many of these tulou’s are being transformed from residential houses into museums. I have mixed opinions about this. On one hand, the 40 or so families that I saw still living in these tulou’s are living in filthy, sewer-less hovels and the new, cleaned-up tulou’s are much more photogenic. On the other hand, the renovated tulou’s feel a lot tackier and less “authentic.” When I visited the old tulou’s, I’d be greeted by old men inviting me to sit down for some tea. When I went to the newer tulou’s, I was accosted by young ticket collectors demanding I hand over Y50.
Anyhow, you can do it as a weekend trip from Xiamen. Take a bus in Friday night, hire a motorcycle driver for all of Saturday and Sunday morning, and then head back Sunday afternoon.