Ok, this put a lot of things into perspective. Just this info is worth gold, I didn't know there was a limit on how many mod I could use at the same time.
There is, and as stated two different limits:
1. amount of "load order" active esp/esm files.
The limit is actually 256 (this is based on there being a two digits code for each one - in hexadecimal two digits means numbering from 00 {zero} to FF {255}) one is hidden (it's for your character save file), one (00) for the Oblivion.esm, and the rest for any extra mods you add.
Wyre bash helps you keep this down with mergeable files, which are now shown in green text, and can safely be deactivated/merged (denoted by a plus sign instead of a tick) once merged into the bashed patch file. And others can be deactivated/imported (denoted by a dot), some of which are in purple text, with only some of their attributes merged into the patch.
2. An upper limit of esp, esm and BSA files in your data folder.
The game won't automatically crash if you have more (as is the case with the above limit) but some will simply fail to load if there are too many.
The limit is not precisely known (and may not in fact be precise at all) but is somewhere between 300 and 400 such files (I run just fine with around 350 myself, just try to keep below 400.)
Wrye can help here with its "Auto-Ghost" feature.
What this does is rename the files that are merged/imported into the bashed patch, such that the data folder doesn't read them as files that go to this limit. While still retaining all that is needed to have them in your game.
How to use it:
In the "Mods" tab in Wyre Bash,
right-click on the "file" heading and select "Auto-Ghost."
Altough now I have a doubt: since I found obmm to be quite handy, I used it to install every mod I have (I created an omod for each and every one of them). Is this going to be trouble for wrye? Should I use wrye bash to install any mod aside from the very big one with scripted omod compatibility info or the like?
Wrye Bash is very good at handling mods that don't require advanced scripts (it can't handle scripts
yet.) But in general OBMM is just fine.
I myself have only recently started using BAIN, as I too started with OBMM exclusively. My suggestion is to do as I do; as you add new mods (which are in BAIN format, simple, or not OMOD scripted) try installing those ones through BAIN (Placing the zipped file or folder into the "...Bethesda Softworks\Oblivion Mods\Bash Installers" folder, and selecting the "Installers" tab in Wrye bash - it takes a while to load up, don't worry
)
Then as you get used to it, you may then choose to export others over to that method.
As Wrye Bash is still being actively improved, it is generally considered that the best course of action is to use it for as much as reasonably practical. But to date OBMM still does have its uses, particularly the scripted installation of complex mods with multiple install options. And a number of the best mods are of that sort. Perhaps one day Wrye Bash will take over there as well, but that day has not yet arrived.
Oh and run BOSS (Better Oblivion Sorting Software) on your files (If activated through Wrye Bash you won't have to un-ghost your files, any other way and you will or it won't work quite right, but you may want to anyway; its faster that way.) Not only does that order your files optimally, it also provides extra bash patch tags (meaning better compatibility/functionality when added into the bashed patch), and an output text file which includes certain tips and advice on what to do with some mods (deactivate/merge, conflicts with other mods etc.)