Like a lot of people here, I think, I'm a beginner who is working my way through 'Russian for Beginners' on my own. I've searched the forum but cannot find any threads about the various lessons and questions/issues/corrections to the practice exercises. (or I'm just not searching for the right combination of words, or something!)

So of course, I have some questions on why some of the translations are the way they are.

I'm currently working on Lesson 8, and the exercises prompted a few questions

1) is there any real difference in meaning or intent between у него есть учебник? and у него ли учебник? The english translation provided implies that one means "Has he a textbook" and the other "Has he the textbook", but my understanding was that there was no real way to differentiate articles and that the two questions are functionally the same. I'm apparently not really clear on when the particle ли is really needed, and when есть is used/omitted. I assume that things will be clearer as I progress.

2) The English sentence "He isn't at home today" is given as Его сегодня нет дома, and I can't figure out why it would be его instead of он -- shouldn't it be in the nom. case?

3) As the sentences get more complex, I'm getting thrown by word order, which isn't explained very well. I know Russian word order is more fluid, since the case endings and such differentiate things much more clearly, but is there a general rule (adverbs before verbs, etc?) that might give me a clue? I understand the use of the particle for emphasis, I think, and the order of negation, but sometimes words like сегодня and плохо show up in the sentence in a place I don't expect.

I'm sure I've got more as I work through things. Having a place to ask questions is great! спасибо!

If there is already a thread for this that I missed, my apologies!