My suggestion is to always buy individual parts, GoodProphets has good prices... And I would try to stick with genuine Joye parts, and not knockoffs. People just buy Joye parts and paint em, so they can charge more for the same gear. Or just try to mimic the parts, and then you're stuck with an inferior product. The Joye eGo is so standard, it will work with just about anything!
The 650mah batt is okay, but the passthrough is more convenient since you can charge it with any mini usb, and vape while you charge. The 900mah is a nice compromise between size and battery life, and the 1000mah is a beast. A little too long for my taste, and doesn't last that much longer than the 900. Choose your atty wisely! The T system is not ready for primetime yet, not at all. The cone atties are okay, but the best atty by a long shot is the good ol 510 with a drip tip. Can't beat it for taste and vapor production. For convenience, I would try clearos too, that's what I use, but some people think they're a pain to fill. They do flood sometimes when laying on their sides as well. It's all about your priorities!