It's... somewhat hard to master it all. Too many interactions, too many opportunities.
>>is it just my bad luck or amount of monsters which do something to my stats or items (corrosion, curse, destroy, etc) is "too many" at start of the game (my highest character level was 17)?
Luck, probably. Depends on which route you take, really. I'm playing Roguelike difficulity, still due to encounter any mosnter which can curse items. Items which are cursed by default or become cursed suddenly on its own... well, to a certain degree it's a part of risk/reward and for some items it's a balance measure.
Scrolls of identification - less common than one would expect. Which may lead to rather spectacular consequences when reading unidentified scrolls from time to time. Part of overall risk.
- of repair - can't recall if I ever seen any, probably, ones I did seen were unidentified and I had no broken items :)
- of uncursing (of curse removal?) - easier than expected, rather than looking for a scroll, you can try to dip offending item into blessed potion of water (holy water, in other words). Who/what is assotiated with blessings?
Stat gain/restore - well, for me, it's a problem too, early game don't provide many opportunities for it. Stats you use often tend to 'restore' over time.
>>Is there some easy way to pass main river near the center of main map?
RUN through Small Cave, then dive through levels below it.
If playing Druid/Ranger, it _could_ be more convenient to take wilderness route instead - less crazy encounters, Survival skill may provide food.
River diving might come handy later, once you'd be prepared to reunite one particular family.
Bridge building will come handy... even more later - unless you'll bump into a river which splits dungeon floor, with no stairs at your side.