The answer to the branded vs assembled question depends on where and for whom. If you don't know much about computers and live in a city where the "branded" company has a firm base of operation, you can go for a branded machine. Otherwise, you can assemble it yourself or get a reputable local assembler to put it together for you. A good assembler will even give you a reasonable warranty.
As to whether the configuration is correct, it depends a lot on what you expect to do with it. You could spend a bit more and get a much better configuration, or you could even lower it and get a mchine that is perfectly adequate for your needs.