Upgrade

Hello,
I'm thinking about gradually upgrading my current transmission..
Currently on a Giant SCR 3 (2007) with Tiagra Rear Mec, Sora triple front and a generic crankset...
I'd like to upgrade to 105, probably starting with the chainset and front mech. Are there any compatability issues I should be aware of? And will I need to change the bottom bracket too?
Grateful for any advice....

This image was uploaded with the post Reynolds launch UK website.

I'm considering upgrading my bearings to ceramic. I'm running Bontrager wheels and drive train - riding for pleasure (not racing) around 300km a week. At GBP170 for SKF hub bearings alone, and more again for the BB, I'm wondering if at the end of a four hour ride I'll truly appreciate the difference. Any advice?

Probably been asked a few times. Apart from I guess a small weight saving which is really not too much of an issue for me. Does anyone think you would gain any noticeable improvement on comfort by replacing an alloy seat post with a carbon one?