file types mainly applications, docs, PDFs.

I would say no. You've stated that you know the disk is small and therefore you intend to use this for Linux. Linux "the operating system" is small; however "data" can be very large. There is absolutely no reason you can't just plug in a USB flash disk of multi-TB and use that for all your data. That is exactly what I do. I have Linux installed, the result is that there are partitions for boot, swap, and root. Therefore my /home is in the root tree. But when I save stuff or download things I end up placing them on an attached USB flash disk. I made no special partition for that, and you don't need too. You take an external drive, use it as is or reformat it to be ext4 (or repartition it to get rid of the manufacturer's included self-ware crap) and just use that drive as your destination for where you store data.

I think redirecting /home to be somewhere else may just cause you complications and extra work. There is nothing stopping you from doing that though.

So, generally the scheme can have three partitions: swap, / root and /reserved space. And the last two can split all the remaining space in half: is that perfectly enough?

They can actually share /swap partition. One can create swap files within the mounted partitions.

Not sure what you mean /reserved space.

Yep, and entirely up to you. Not even techically reserved IMHO, just unpartitioned. Plenty of opinions about how much is fine for a Linux install, throughout this thread. You therefore should choose how large to allocate for your root based on the inputs you've seen and the amount of space you decide you feel makes sense for you. The rest I would just leave as unpartitioned space since you're expecting to use that for another potential Linux install in the future. That future install will detect unpartitioned space of some size and likely ask you if you desire to use some or all of that space.

Where should be installed boot loader when install Linux on an external ssd drive? Should it be on hard drive's root partition?

You should install to external drive. If you install to inernal you will have to keep drive connected just to boot your main OS.

what options to select when boot from Debian 7.6.0 "netinst" CD, there is no Live desktop, it immediately ask to select an installation, without asking where I want to install Linux.

Install
Graphic install
Advanced options
Help

Didn't it ask you how you want to partition?

It shows the above menu.

Select "Advanced Options>>Expert Install" that way you can select where you install bootloader. It's a series of questions follow them, especially network setup, if netinstall.

At which step disk detection should start?

It will be a few steps after wireless & user setup.

The installation process is somewhat unclear, I have a few issues:
1. The first issue is when detect network hardware:

"Detect network hardware:
Some of your hardware needs non-free firmware files to operate. The firmware can be loaded from removable media, such as USB or floppy(!).
The missing firmware files are: rtl_nic/rtl8168d-1.fw
If you have such media available now, insert it and continue.
Load missing firmware:
No / Yes.

I choosed No, then setup continued: what then the point of this, if setup continues without a firmware file?

2. Next unclear point is when Setup offer to load or not anadditional modules, there was specified partman, Master Boot, etc, among others. Should I load some modules? I choosed to load partman and two other modules since there was no directions what type of installer will be used.

3. Next unclear point is Partition disks.

I'm unsure of the steps I must follow here to install. I selected "SCSI5 (0,0,0) (sdb) - 60GB Kingston" (my SSD), then "Continue", and it brings to the following step:

Can't find clear manual on this debian install, as all steps are significantly different for each setup package.

Obviously drive is unformatted, select msdos.
For the network you can install after completion or try to copy the driver to cd, something I have never made work. I usually use my android phone for network debian detects it.