any tips for drilling into plastic and/or adding peg holes?

[Dkaris]

Pick up a pin vice. Perfect for this type of thing. Most will come with a number of small drill bits that come in very very useful.

[snaketales]

Thurmus has given lots of good ideas. The only other thing I can suggest is use a drill but slightly smaller than the post you want to insert and use that to widen the hole if needed.

There are plenty of other customisers on here who may be able to help too.

Good luck!