Not sure what "ESBox" is. If you're talking about "Scratchbox", no you don't HAVE to compile in it. If you can set up an armer-targetting compilation toolchain with all the right dependencies, more power to you. I tried that, and got raped by things far outside my level of tech savvy.

So scratchbox, set up in debian with the Nokia provided auto-installed, is probably the most convenient way to start compiling.

make sometimes gives errors which can be ignored. Sometimes not. It depends on a lot of stuff.

make is just a convenient way to compile a package, instead of running more manual compilation stuff. Basically, think of it as a macro including compilation and other stuff. Programs by default install their binaries/man-pages/etc to some directory. Most of the time either ./configure or make let you pass a command like --prefix=[path], where [path] is wherever you want to put the directories/files/binaries.

In order to find the binary if you didn't use a non-default prefix, is to logically search all the places where it could go: /bin /sbin /usr/bin /usr/sbin /usr/local/bin /usr/local/sbin, etc, etc.There's also this magical command called "find" in Linux. "which" can also help you find commands whose binaries or symlinks are in your $path, and command tab-auto-completion plus logic plus guesswork is good at figuring out what the command actually should be called. (Keep in mind scratchbox has to be targetting ARMEL - if it's set to target x86, or whatever, it will compile the wrong architecture and you won't be able to run it on the N900 itself.)

You can't make a .deb file without either A: manually building them using tar + gz + ar, which I assure you is ridiculous, and/or using specific tools for it, such as "dpkg-buildpackage". dpkg-buildpackage by default produces its output .deb and source files in the directory about the one you're building.

In the future, help yourself - nothing I just said couldn't be found with a couple of minutes of google searching for each question.