I do just 1st steps and get Reaper crashed while scanning VST.
I entered 2 paths to VST folders: Sonar and Steinberg and start the scan, after few minutes I get it crashed (see the screens). And VST scan window has these settings

 

culprit is usually some corrupt plugin, I can see you're still using obsolete DirectX FX format instead of VST?
you can open Reaper again, scan other plugins, and either ignore failed plugins, or you can manually rescan them individually

 

If you're stuck in a crash loop, I'd start from scratch with 0 plugin folders. Add half the folders back. If it doesn't crash, add half of the remaining half of folders. If it does crash, remove half the added folders. I'd use smaller subfolders once you've narrowed it down.

 

I also moved from Cakewalk Sonar years back, I had no issues with their plugins being used in Reaper,
if you used Dark Tungsten theme in Sonar, you can use Echolot theme for Reaper:
https://stash.reaper.fm/theme/2864/Echolot_1.12.ReaperThemeZip

btw I see you're not using latest Reaper version, 7.0 is fairly old by now, so they might have ironed some bugs since then,
and don't use relative paths and plugin data paths, only locations of VST and VST3 plugins themselves

 

I installed latest 32 bit version from their site.

I use them both cuz, for example, nobody invented something multichannel as Edirol Orchestral till today

I have Sonar and Acoustica Mixcraft installed along with Reaper, but they both accept each other plugins as well as 3d party ones too...but Reaper doesn't
And more, I unchecked the box "scan the plugins at startup", still Reaper does it, why?

 

do you have a 32bit system? if not, you can use 64bit Reaper and open 32bit plugins there
in your screenshot I see 7.0 which isn't latest, 7.15 is..
Edirol Orchestral (latest final 1.03) is VSTi..
maybe you're pointing it in wrong folder? order of paths matters, and also Reaper may hide multiple plugin formats when scanned more of them,
Reaper will try complete scan of plugins

 

Ok, let's see it in details:
1. First thing I did - ordered Reaper scanning folders: Sonar and Steinberg (2 folders and NO MORE!)
2. Reaper did it all and I closed and then open it again, I checked out its
VST folder and found that's ok - all I need, is there
3. I start a new project and want to choose some VSTi...once I press the VSTi name, Reaper starts scanning the folders I didn't picked before and crashes! But, I didn't ask this action, what the heck!

Yes, I have both 32 and 64. I have 2 Win systems on the same machine - 32 and 64bit, I installed 32/64 bit Reaper on each system accordingly, and started with 32 bit cuz I have a lot of old Sonar projects wich I hope to open in Reaper with a special script... and this's a reason, why I need all VSTi and Direct X plugins that I have on those Sonar projects

 

Why so complicated? Reaper can output a crashlog.

 

This is how I like to do this also, especially with Logic. Once AUValtool tries to validate a plugin that crashes it; anything it has not scanned yet does not get scanned, and everything scanned will get scanned again. You can check each batch, you can move them into a folder so they are not scanned again. If you have a thousand plugins to scan, this is the fastest most systematic way.

 

this is only problem on Mac which can use AU plugin components, recent MacOS versions may refuse to load AU plugins without reboot,
but OP is on Windows, so no such issue luckily

 

Works fine on my 5.1 Logic 10.4. 32 Lives still works and REAPER can use AU on Mac. Another timesaver is being able to codesign every plugin on the machine in 4 commands and then forcing validation for all of them in a single swoop. But you are right, some will never show up until a reboot. It is very few, and seems random; but it's usually older ones. If you leave it till the end, you can do 1 reboot.

I like the validate and hide method @xorome mentioned so you are not rescanning lots of stuff.

 

How to do this?

 

It is an optional setting during the Reaper installation. If you missed it, reinstall. No uninstallation necessary.

If Reaper has a hard crash at some point, for example when scanning plugins, a dump file is created. Open and read the dump file to find out what caused the crash. Done.

 

Where is it located?

 

Good question. It's been a while since my last crash.
Search for .dmp in C:\Windows

 

Ok, I see no real ways to fix it forever, so I found a simple trick:

as it was before, once I choose a VSTi to add, Reaper starts scanning, then I immediately press "Cancel" on a scan window...
it works, no crash so far