Mostly I play game without guide but in old games like this I always more cautious.
So I like to ask some question...

1. Maybe there is hidden stats about hit chance? I got greatsword and it looks more hard to hit. Or I should put off my shield or something?

2. After reach 4 level, leveling is much harder than before. I gain some exp but I didn't get any level after 4. Is this normal 'soft cap' for this game?

Pardon my broken english if it bother you. But I can't find any information on my language.

I have noticed the same, but don't know much about the internals of the weapons. There is a hintbook available for download which might have some info in there (there's a previous thread pointing to this) This is normal. It's possible to get to 5 and 6 with a lot of grinding. But higher than that would be pushing it (except with certain items). From memory you need a rogue skill of 5 to pick certain locks in the game, but higher than 5 is not required for anything in-game as far as I remember.

It is important to choose an appropriate weapon for each enemy type. Some need to be dispatched with blunt weapons, some with cutting or piercing. Sometimes it doesn't matter much which type of weapon you're using, sometimes it can be very hard to hit an opponent and even if you do, you won't be causing much damage.