Generally, you don't - as 1. the characters tend to be too complex and 2. vanities are not guaranteed to be unique.
There was a service that did not rely on third party servers to map a short string to a guaranteed unique address (by being the very first such address in the blockchain): FirstBits.  Most common words+extensions were quickly generated though, so at best you might still be able to find a 'FirstBits' type address like 1QuehqQ (no idea if that already exists), which isn't that much easier to remember.  FirstBits quickly went out of vogue and most sites no longer support it.

Several - see earlier in this thread - but you'll generally have to pay for it, and 8-10 characters is quite costly.

With case insensitive you can reduce the time to find a patter alot, if you are happy with it.

Without digging into the exact numbers here, keep in mind that you can't have BTCCOM as it contains an 'O' (uppercase letter 'o'), which is forbidden

I personally used it to generate 4 addresses with custom words in the beginning !
Thnx, a great service to have a great btc address

32 variants, yep.

Though realistically - or rather, aesthetically - speaking, not all of those are going to be pleasing.  That loops back to K1773R's "if you are happy with it".

I.e. (to me)
1bTc888coM, 1btC888coM, 1BTc888coM - just don't look right.
1btc888com, 1btc888Com, 1BTC888com, 1BTC888Com, 1Btc888com, 1Btc888Com - look okay.
1BtC888com, 1BtC888Com - might be okay too.

So 6, maybe 8 candidates.  Though if one were looking for those 6/8, they might as well store any of the other 32 matches in case of a change of mind later on

NVidia drivers keep crashing constantly with vanitygen. I've tried with several, and they all crash. The crashes are random, so I can't really help in debugging as I cannot reproduce the bug... So I started assuming it's normal behaviour Sometimes it even causes artifacts on the screen, and a reboot is required.

As for the error you refer, I've never seen it...

Can i run vanity miner using cpu , without opencl

A distributed Vanity Address generator might be faster, dividing work across all GPU's instead of one work per GPU. There are lots of distributed designs out there already, some open source but for CUDA, would need to convert CUDA language to OpenCL language. This would make it easier for those with large farms to utilize an address generator without it being a PITA to setup.

I need keyconv, does anyone have it? the latest version come without the keyconv

Kangaderoo's repo has a Windows build:
https://github.com/kangaderoo/vanitygen/tree/master/WIN32Build

A GUI probably wouldn't help with your problems.  Would probably need somebody to look at the GPU code and figure out why it's not working properly for that card ( I seem to recall you asking about the 280x before, so I'm assuming you had no luck with existing info. )