To answer your questions:
A 15kHz CRT will display 240P like original, but higher res things like EGA/VGA will be displayed in interlaced mode which will not look as good. You'd also need a TV capable of RGB signals, which are easy to get in Europe, but not in the US. Google groovymame and crt emudriver.
LCDs are fixed resolution so everything needs to be upscaled, which MAME does fine. 240P games will never look 100% authentic but modern games are a blast. Note that this setup needs a very good graphics card, as opposed to the easy requirements of a CRT. Google HSLS and CRT shaders.
Good luck!