For development, 8 or even 16 GB would be great, and look for the higher-res screen.
Anyway, for $200 you can have a very decent, durable, highly compatible machine. The only functional thing lacking would be a Thunderdolt port.
[0] https://forums.lenovo.com/t5/ThinkPad-T400-T500-and-newer-T/...
[1] http://pcpartpicker.com/products/memory/#t=9&Z=16384002&s=30...