pcb design / pin connection guidelines

No specific recommendations, but...

With any new chip I check the user manual and data sheet for how to deal with unused and power pins and also look at the schematic of any demo boards available.

You will often find the demo boards don't follow the written recommendations, some times the written ones aren't even possible (I used a ____ brand chip as an example at a trade show panel discussion about this, a 12mm x 12mm chip was supposed to have 24 capacitors DIRECTLY under the part, this included a mix of tantalum and ceramic).

The LPC parts are nice as they have the core regulator built-in, no worries about sequencing up multiple supplies on the board (especially when every chip says it has to be the first to power up).

I use good power/ground planes, a reasonable decoupling capacitor at each power pin, and some bulk capacitance on the board. These parts don't draw nearly the power that older parts did so that helps a LOT. I designed a VoIP board that drew 25 Watts and every other part on the board needed its own power supply. I had an FPGA just to sequence everything on.

decoupling depends on the PCB design also, so is not a simple answer.
Clocking is simple as the device has an internal RC oscillator that it uses at startup so you can choose almost anything, the PLL is very flexible so you only need to ensure you meet the frequency stability requirements for USB.
Pins for an interface is not a simple answer either as most interfaces have multiple pin selection options, the device is VERY flexible in this respect. The starting point is make a list of what signals you need, each section in the UM usually defines what is the minimum requirement, then use a spreadsheet so allocate these to available pins. Start with the EMC since these pins have the fewest options in terms of multiplexing. It's a tedious process.

The device seems to consume < 200mA with most functions operating, and has an internal regulator which helps, I've not seen any issues with power supply design for it just using a variety of different LDO's, it always seems to boot correctly so that does not seem critical.

I've been referring to the Hitex A4 schematics (http://www.lpcware.com/content/nxpfile/lpc1800-lpc4300-hitex-board-schem...) for the basics. However, it doesn't seem LPCXpresso 4.2.3 is far enough along yet to assist in planning pin assignments or enabling/disabling clocks and peripherals---at least for me the example dual core project loads up with empty core register and peripherals tabs (http://support.code-red-tech.com/CodeRedWiki/LPC43DualCoreProjects). Anyone found an efficient way of dealing with this? Having poked around a bit it seems like the current options are to either dig through the header files to figure out how to get things set up (probably not too bad if one's worked with other Cortex parts, though that's not the case for me) or wait for 4.2.4.