As far as I have been reading tutorials on this site it is recommended to separate Windows/ programs and Documents into separate partitions. So I am going to create C- partition for Windows and Program Files of about 100MB.
Obviously a typo there... you clearly meant 100GB, not 100MB, right?
At 100GB you'd have plenty of room (maybe much more than you need) for Win7 itself, which depending on how many and the type of programs you install would use probably 25GB-45GB. I'm guessing closer to the lower number for you, but I don't know.
Thus the rest of the space would be available for the \Users folder, which is the old WinXP "Documents and Settings", where documents and other data typically get stored by default (unless you specifically choose to save things from your work into genuine "data" folders you've created, maybe on other drives or partitions).
The advantage of putting "data" off of the C-partition is that it is more easily preserved should you need to reinstall (or restore from a "system image") just the operating system on C. Your "data" is untouched over on D. Of course if you had to replace the entire hard drive, that's another story. But that's what second internal or even external USB hard drives are good for, to segregate data from Windows to make it easier and more organized for you to backup and restore if you needed to, as well as a much simpler job of reinstalling the OS.
Win7's allows you to incorporate your external "data" folders into "libraries", so that you're not limited to such finite constructs as "My Documents" or "My Videos" or "My Pictures" living strictly in the \Users folder architecture on C. Of course, there's a strong urge to simply name these "data" folders elsewhere with more meaningful and "professional" and intutive names, other than "My ...something". Of course you can just navigate to them, for opening and saving... you don't even need to make them part of "Libraries" if you don't want to.
What about the other partitions. Is it worth to create separate partitions for say for "Images", "Documents", "Development Projects". Or is it better to put all this stuff into one partition?
Mostly a matter of personal choice. There is no such thing as "better" here.
What IS better is definitely to get your data out of \Users and off of C, which is the first step most people take when then begin to outgrow a single-C environment.
Don't forget that part of the "maturing" out of single-C is also to be absolutely certain you have an adequate backup/recovery scheme in place, to preserve your critical data from destruction or loss. You don't want to be devastated and cry if your machine dies (especially if your one-and-only hard drive dies, if that's also what you were using for the target folders of your backup scheme).
External USB drives today are large and cheap, and are excellent solutions for a proper and reasonable disaster recovery plan. Windows provides its own built-in backup features (especially "system image", which is terrific for the C-partition) but you may want to investigate 3rd-party products that provide more extensive or elaborate and sophisticated backup/restore technology.
Advantage of multiple partitions, as I see, would be more flexibility for backup/recovery. From the other side, disadvantage of multiple partitions would be not optimal usage of disk space. What are the other considerations?
See my remarks above.
I think a good investment would be another drive, namely an external USB drive, to be used for your backups. There's not much real security in using multiple partitions of a single hard drive for such a task, not to mention the performance hit of backing up from one partition to a second partition on the same physical hard drive.
Lots to think about.
You should definitely
download and install Partition Wizard Home Edition v6.0, as well as the standalone boot CD version which you can
burn from this ISO. This is the product to use, to accomplish everything Windows' Diskmgmt can do plus lots more.
