Welcome to Orwell Dev-C++'s severely neglected help file! You can start navigating it from here.
A: You can of course. If you want to use a 32bit MinGW compiler without having to set paths, you can put it in a 'MinGW32' folder next to Dev-C++ and force a first start by removing your configuration files. This folder will be recogized and paths will be automatically set. 'MinGW64' is the auto-detect folder for TDM-GCC x64 installs. One can also easily install compilers anywhere and manually create a profile in Tools >> Compiler Options >> Add. You must then set manually Directories, Programs and optionally Settings.
A: Sure. You can toggle them in Tools >> Editor Options >> Show Editor Hints.
A: There aren't that many differences at all. I've decided to support relative paths for (example for) compilers in all versions: a macro called %path% is used for paths containing the location of devcpp.exe. So using paths in Dev-C++'s folder will make these paths use this flexible macro. The trick of the portable version (devcppPortable.exe) is that it tells Dev-C++ to put its settings in a location called .\config by using the supported -c flag (i.e.: -c ".\config\"). This will preserve settings when moving an install around. Of course, the portable version is smaller thanks to 7-Zip's LZMA2 (the installer uses LZMA1). Also, you don't have to download the setup overhead.
A: Yes, it's taking very long, thanks to the huge amount of headers supplied by TDM-GCC x64. Of course, no single programmer will ever use them all. I suggest selecting the custom caching options or navigating to Tools >> Editor Options >> Class Browsing >> Completion. Add the headers you often use. You don't have to add everything manually fortunately. Adding windows.h for example will include the whole massive heap of Microsoft stuff referenced inside that file.
A: First off, you need to pass '-m32' to the compiler. To do that, go to Tools >> Compiler Options >> Settings >> Code Generation and set pointer width to '32bit'. This sets the global option. Projects override this option, so for every project already made, go to Project >> Project Options >> Compiler >> Code Generation and set 32bit here too. As a last step, you need to tell the compiler to use the 32bit libraries. Go to Tools >> Compiler Options >> Directories >> Libraries. Edit the 'lib' path to point to 'lib32'. That's it. You're done.
A: Simply put, the 64-bit version can do everything the 32-bit version can, and more. Dev-C++ itself is compiled for 32-bit systems and can always be used on 32-bit systems. The compiler itself can for the same reason also be used on both architectures. The 64-bit compiler (TDM-GCC 4.6.1) can create both 32-bit and 64-bit (the latter one is default) executables using -m32 and -m64 (see Compiler Options >> Settings >> Code Generation). Of course, you can't run executables created with m64 on a 32-bit system. The 64-bit compiler comes with a lot more headers and libraries, including fancy stuff like the Windows Aero (DWM) API. The 32-bit compiler (standard MinGW) is more conservative, lacks some shiny features, but more thorougly tested.
A: When compiling for 32-bit, you also need to point the compiler to the 32-bit libraries. By default, the compiler is pointed to the 64-bit ones. To fix this, go to Tools >> Compiler Options. Select your 64-bit install. Then go to Directories >> Libraries. Then double click the path pointing to the 'lib' folder. Edit it to make it point to the lib32 folder next to it (just add '32'). Then click replace. Done!