my 2 cents, wachana nayo, especially if you are not the headmaster of a certain school;
for the above points,
1. yes you open an account with the publishers (at least for the local ones),
2. For the returns; ehhh! most of the publishers will give you the books at between 15% and 30%, of course depending on the volumes you can move and your negotiating skills - though I know one of the big retailer back when I was selling books used to get at around 50%.
its a stressful biashara since the only books you can sell now are school text books, and with the used and passing down the demand is not very high siku hizi.
Another complexity is the number of different text books that have filled the market, that means you will need to stock much more books, and considering very few or none of the publishers will give you the books on credit at first the investment can be steep with no promise of returns.
add the fact that schools are recommending different books, the photocopiers and the cameras which are constantly used to take photos and save on laptops where reading takes place, plus the same new books being sold at a fraction of the cost on some street corners (piracy).
To crown it all, if ever the government laptop thing gets going, you will be staring at a museum.
lakini if you are still determined, make sure on top of the books you focus more on the stationeries, also if possible ongeza uniforms, and if you can sell some cheap ereaders - in short open a one stop school retail center.