Welcome to genvibe! There is a ton of info you will find by searching, but here are some.This one
http://forums.genvibe.com/zerothread?id=9803has pics from my spring and wheel install I just did over a week ago. Tein S-Tech springs with a 2.2-2.5" drop. I'm very happy with them and you can get them for about $140 shipped from Adventon.com or off ebay.To answer your 1st question, it's not that difficult. Here is a link to some good instructions. It would really help if you can have someone help you.
http://forums.genvibe.com/zerothread?id=4918 2nd question, well, not sure which is the best. Everyone probably has their opinion. The S-Techs have a large drop, at first I thought maybe it was too much for me, but I really really like it now! The ride is still very smooth and comfortable and you do have to be more careful with clearance, but it's still high compared to other types of cars with a drop. It's only like 1/2" lower than my Dad's stock '93 Honda Accord, so it's not that low since it had a high clearance stock. Here is a link to a topic I made to help decide on my springs:
http://forums.genvibe.com/zerothread?id=9521.3rd question, check out my pics, that's with a 2.2-2.5" drop. I forgot to measure before, but Tein says a 2.2" drop in back and 2.4" in front. The TRD and Eibach Pro Kit are the same and only drop about 1.5".4th question, I'd only go with 18s. That is what I have and I think they look perfect! 19s would have a thinner profile and could be damaged more easily plus they are even more expensive.Later,
Justin 2003 Vibe GT - Mille Miglia Evo5 18x8 Wheels (now stock)- Magnaflow Cat-Back Exhaust (now stock)- Tein S-Tech Springs (now stock)- Injen CAI - Red Painted Calipers - Hella Supertone Horns - Polk Speakers - Bazooka RS8A-HP Sub - Kenwood Headunit - Still love my Vibe, but I've just turned it back into a basic daily driver.