of course up to you, but my recommendation would be to use as many apps/libs from existing extensions as you can, because those are known to work with tinycore.
As an example, maybe something from the rpm is looking for a file in /etc, rather than /usr/local/etc
$ tce-load -i qt-4.x-base qt-4.x-webkit qt-4.x-opengl
$ ldd /opt/google/earth/free/googleearth-bin
linux-gate.so.1 => (0xb78de000)
libpthread.so.0 => /lib/libpthread.so.0 (0xb78bf000)
libdl.so.2 => /lib/libdl.so.2 (0xb78bb000)
libgoogleearth_free.so => /lib/libgoogleearth_free.so (0xb77c8000)
libQtCore.so.4 => /usr/local/lib/libQtCore.so.4 (0xb74ae000)
libQtGui.so.4 => /usr/local/lib/libQtGui.so.4 (0xb6a07000)
libQtNetwork.so.4 => /usr/local/lib/libQtNetwork.so.4 (0xb68ce000)
libfontconfig.so.1 => /usr/local/lib/libfontconfig.so.1 (0xb68a0000)
libfreetype.so.6 => /usr/lib/libfreetype.so.6 (0xb683c000)
libcurl.so.4 => /usr/local/lib/libcurl.so.4 (0xb662d000)
libX11.so.6 => /usr/lib/libX11.so.6 (0xb652c000)
libXrender.so.1 => /usr/lib/libXrender.so.1 (0xb6523000)
libXext.so.6 => /usr/lib/libXext.so.6 (0xb6511000)
libGL.so.1 => /usr/local/lib/libGL.so.1 (0xb6426000)
libGLU.so.1 => /usr/local/lib/libGLU.so.1 (0xb63ca000)
librt.so.1 => /lib/librt.so.1 (0xb63c2000)
libQtWebKit.so.4 => /usr/local/lib/libQtWebKit.so.4 (0xb50ae000)
libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0xb4fec000)
libm.so.6 => /lib/libm.so.6 (0xb4fc9000)
libc.so.6 => /lib/libc.so.6 (0xb4ebe000)
libgcc_s.so.1 => /usr/lib/libgcc_s.so.1 (0xb4ea8000)
/lib/ld-lsb.so.3 => /lib/ld-linux.so.2 (0xb78df000)
libIGCore.so => /lib/libIGCore.so (0xb4db7000)
libIGUtils.so => /lib/libIGUtils.so (0xb4d8f000)
libapiloader.so => /lib/libapiloader.so (0xb4d8b000)
libauth.so => /lib/libauth.so (0xb4d1c000)
libbase.so => /lib/libbase.so (0xb4c2f000)
libcommon.so => /lib/libcommon.so (0xb4b94000)
libcommon_gui.so => /lib/libcommon_gui.so (0xb4b70000)
libcommon_platform.so => /lib/libcommon_platform.so (0xb4b6b000)
libcommon_webbrowser.so => /lib/libcommon_webbrowser.so (0xb4b23000)
libcomponentframework.so => /lib/libcomponentframework.so (0xb4b1c000)
libgeobase.so => /lib/libgeobase.so (0xb4827000)
libgeobaseutils.so => /lib/libgeobaseutils.so (0xb47d9000)
libge_net.so => /lib/libge_net.so (0xb478d000)
libgoogleapi.so => /lib/libgoogleapi.so (0xb4771000)
libmath.so => /lib/libmath.so (0xb472a000)
libmoduleframework.so => /lib/libmoduleframework.so (0xb471c000)
libport.so => /lib/libport.so (0xb4713000)
libprofile.so => /lib/libprofile.so (0xb470f000)
librender.so => /lib/librender.so (0xb46bb000)
libreporting.so => /lib/libreporting.so (0xb46ae000)
libsgutil.so => /lib/libsgutil.so (0xb4591000)
libspatial.so => /lib/libspatial.so (0xb43a4000)
libxsltransform.so => /lib/libxsltransform.so (0xb439f000)
libz.so.1 => /usr/lib/libz.so.1 (0xb438d000)
libgthread-2.0.so.0 => /usr/local/lib/libgthread-2.0.so.0 (0xb4389000)
libglib-2.0.so.0 => /usr/local/lib/libglib-2.0.so.0 (0xb4283000)
libpng12.so.0 => /usr/lib/libpng12.so.0 (0xb4266000)
libSM.so.6 => /usr/lib/libSM.so.6 (0xb425e000)
libICE.so.6 => /usr/lib/libICE.so.6 (0xb4244000)
libexpat.so.1 => /usr/local/lib/libexpat.so.1 (0xb4224000)
libXau.so.6 => /usr/lib/libXau.so.6 (0xb4221000)
libXdmcp.so.6 => /usr/lib/libXdmcp.so.6 (0xb421b000)
libIGMath.so => /lib/libIGMath.so (0xb41d2000)
libgdata.so => /lib/libgdata.so (0xb41bb000)
libfusioncommon.so => /lib/libfusioncommon.so (0xb41b6000)
libIGAttrs.so => /lib/libIGAttrs.so (0xb4134000)
libIGGfx.so => /lib/libIGGfx.so (0xb3da0000)
libIGSg.so => /lib/libIGSg.so (0xb3c98000)
libuuid.so.1 => /lib/libuuid.so.1 (0xb3c93000)