Generally I agree with the advice of follow the manual, but I changed my manual tranny oil and diff at some point (earlier than the manual) and the tranny definitely feels noticeably different (better!). I think it can't hurt to do this early, the only negative could be spending $ you don't *need* to spend, but it does make it shift nice. That and MTEC springs =
I went with Motul Gear 300 for both, it was not hard though you have to get the whole car off the ground, and level!!! Threads in the maintenance section about the specifics of doing so. I'm in SoCal and the only difference I notice in a negative way is for the first few minutes in the mornings, it can be hard to downshift into 2 & 1. 5-10 minutes in it is not a problem and even when it is cold it'll still go, just takes a bit of effort. I've never felt like I'm pushing anything that causes damage though. Just don't downshift for the first few minutes and no issue. It upshifts just fine.
For oil, I wanted to try the high end stuff to see if it gives me wood, so I went with Eneos Sustina. So far, I like it but tough to say without time and chemical analysis if I'd say it was worth it or not.