Etosha self-drive without guide

yes and yes.

Agreed, yes and yes. Camp inside the park so you can hangout around the waterhole in the evening and stay in Dolomite for at least one night if you can afford it.

i can only repeat, yes and yes :-).
and its actually very "easy" to find animals, as etosha is basically a huge saltpan, with plenty of small waterholes, and the animals of course tend to go to the waterholes to drink. so you drive around the park, drive to a waterhole, and see what happens etc.

and as pointed out by frof, stay in the park. the 3 "cheap" (but still very good) restcamps okaukuejo, halali and fort namutoni all have a waterhole infront of them, and you can sit there in the early morning or in the evening (when the day visitors are gone) and observe the wildlife. and if you want a splurge, stay at dolomite for a night (or better 2 nights).

Yes, it is easy and advisable.
Roads are gravel, but usually in good condition in winter (dry season).
Wildlife is easy to sight even if you're not very skilled.