Thanks, Jake, for your replies and helpful tutorials! I've finally gotten Yosemite to install and boot fine on my T410 with 1st gen Intel HD Graphics. The main difficulty was that my laptop randomly boots even with the wrong framebuffer kext on the installation USB. After days of trying, I ended up using the Alternate one and the installer boots consistently.
One thing is curious though. After installing successfully, I constantly got a black screen upon boot, and had to use a working Mac OS X located on another partition to install all the AppleIntelHDGraphics*.kexts into the Yosemite partition.
With the graphics kext out of the way, the rest of the issues were newbie-related. Eg. not booting with -f after installing kexts -> it doesn't boot -> wrongly assumed it was a graphics issue again. Now I learned to use -f after any installation of kexts or system updates. It was a slow process installing and testing kexts one by one, but I've finally got the keyboard/trackpad, audio, ethernet, WiFi via USB, AppStore (ethernet was not en0)...
Maybe I'll slowly tackle the other issues, like sleep and hibernation...