If you haven't already unlocked your bootloader, then yes, you will lose everything. But all if those things you mentioned can be backed up and restored after you've completed the process but you do have to copy the pics to your PC.

Most Roms in my experience have improved battery life, and improve even more when paired with a nice kernel. Ever since I got my GNex, the first month or so I had it at completely stock, I was barely able to get through a day of usage. Most days I'd have to charge it in the middle of the day. But ever since I rooted I can now easily get through a day and then some. For the record, I'm currently running the LiquidSmooth 1.3 rom with Lean Kernel 2.8. Playing with rom/kernel combos will yield the best results because all phones are different.

Most roms now are working off of the leaked 4.0.4 build and the radios are said to have better signal strength and improved 3g/4g hand offs, so that could also improve your battery life a bit. As for 4.0.5, nothing yet. But if possible, keep your phone on wifi for as long as you can. Its the biggest benefactor to your battery and will exponentially improve your battery life. If you can't do that and speed isn't as important to you, then just switch off 4g and stick to 3g because LTE kills.

Other than that, I hope you decide to root because I was like you and afraid to lose everything, but once I got past that fear, everyone on this board was so helpful that it made the entire process so much easier for me, so don't be afraid to ask away if you have any questions

 

enjoy

 

The smoothest, most reliable roms that I've heard of are AOKP, LiquidSmooth, and BAMF. The others, IMO, are mileage may vary and depends on the user, but these are the ones I've heard the best, most stable experience from.

 

i personally dont think anyone needs to be convinced to root their phone. its your choice, 50 people could say its a bad idea, and you would do it anyway because your mind is intrigued of as to why.

 

I read that something called "Jerry's backup utility" can backup everything before unlocking and rooting.

[BETA] Backup Wonder Machine (no root, ICS only) - Android Forums at AndroidCentral.com

 

I didn't use it, I was just relaying.
I also read wugs root toolkit could do it.