Do look around. I just bought mine less than 2 months ago WD Passport 500GB around RM300 at Lowyat. Maybe what you can do is to look at the GS and ask them how much is the shipping to where you are.
FW is truly very fast but as for me where I only store my movies, pictures, tunes etc it proves to be fast enough. As for backup I would do it during the night and just leave it. I thought of having FW HDD before after thinking much I don't need the speed at all (although its nice to have it). I'd rather have the saving and maybe get 1TB or 2TB desktop size later on and it can serve as final archiving place. Plus the very much fact that I don't do any image/video editing so I won't be truly taking the speed advantage that much especially all in there are for leisure

1) Any extra HDD will do. Rule of thumb is that the backup cannot be inside the current disk or else it won't be a real backup anyway. Some bought new bigger HDD for their mac and use the one supplied with their mac as backup drive. Just need some enclosure will do the trick. Some get an external FW or USB drive. Browse through all your options.

2) No idea. I usually dictates it based on my wallet and my need. Currently I have 500GB 2.5" drive. Plenty of space for all my movies and music plus it's portable since I really need that function. If you don't do alot of movement get a 3.5" drive as it's cheaper and can get more disk space. 2 partitions one for TM and another for storage space for all those movies/musics/pics. Make sure it's bigger in capacity that your current drive if you plan to use TM with that.

3) Alot of freeware programs available. You can use all those like make image, just backup certain path/files. Example SuperDuper! Head to freemacware.com to get ideas. Depends on your need
TM can do those plus more customization but more of a backup purposes where the files constantly change. Image is taken that point in time thus more suitable if you plan to have a duplicate disk or restore whole ISO etc. Well that's my preference anyway.

Think carefully now.
I have tonnes of files more than 4GB since I have lots of HD movies. With this type of screen, makes watching movies and seeing photos exciting (though I doubt one photo can take more than 4GB..hehe) Alot of my movies are around 4-5GB per file. Also I have alot of ISO images with me.
Moving ahead with changing the file system can be pain in rear especially if you need to move around files and you don't have extra disk space in current laptop to kick to or extra HDD to put it form temp