Re resolution: The most important point is that you're scanning a
printed picture, i.e. a screen. Depending on what you intend to do with
your scan, there is a big chance that the result will show an unsightly
moiré pattern.

If your scanner software has an "unscreen" feature (the name of this
function varies with the software), then check it and insert the screen
frequency (probably 150 lpi for a magazine). With some programs, this
function works as advertized, sometimes it does not. If it does and you
don't want to enlarge the picture, there's no point in scanning with
more than 300dpi (or even 72 dpi for monitor display).

If your scanner software doesn't have this function, then things can get
tricky. Usually you'll get the best the results scaning with very high
resolution and downscale afterwards. This approach requires a bit try
and error.