wow... lol...
Q1 - HTIB is cheaper but getting one so cheap that it doesn't come with Optical input is a no-no.
Q2 - BD Players are now quite cheap. Skip the PS3 if you don't play PS3 games. Get the PS3 if you do play PS3 games
Q3 - You won't be able to play downloaded HD movies (MKV files) on your external HDD using your PS3. You may want to consider getting a Media Player.
I have this problem with a setup similar to yours. 32" LCD TV, PS3, Media Player and HTIB. I have to manually plug and unplug the optical cable from my PS3 to Media Player each time I use 'em (PS3 for BD and Media Player for softcopy HD movies). To avoid this issue, spend more... get a proper AV system with multiple HDMI inputs.
Then again, a Yamaha / Pioneer / Denon AVR system in a small room can be quite an overkill. Alternatively, you may want to consider a BD HTIB (BD player that comes with 5.1 sound system and an Optical Input). Then your setup should be:
- Media Player --> BD HTIB via Optical for Audio
- Media Player --> LCD TV via HDMI for Video
- BD HTIB --> LCD TV via HDMI for Video
- Audio comes direct from your BD HTIB
Sample BD HTIB that I know comes with Optical
http://www.sony.com.my/product/bdv-e300 (RM2499)
http://www.sony.com.my/product/bdv-e800w (RM3499)