Correct way to tile outdoor concrete pad

I have been reading this forum and others to make sure that I do my outdoor tiling project correctly. It is a small concrete pad outside my back door, 42 inches square. Now that I have finally (I think.) have a tile pattern and sizes figured out (4x4 border with 12x12 diamond pattern inside) and tile (unglazed porcelain), I want to make sure I install correctly.

1) Do I need a waterproofing membrane? I live in Maryland so there is freeze/thaw, but the pad is covered by the deck above (still gets wet though). I have looked at Nobledeck (expensive) and some roll-on Tec product (forget the name right now). Is a waterproofing membrane (either sheet or liquid applied) necessary?

2) What is the correct thinset/mortar to use? Unmodified with latex additive? I found a source online that sells small tubs and bottles of the Kerabond/Keralastic system (mentioned in many forums). Most places have 50 lb bags, which is way too much for this little job. There is a tile store a little ways from my house that sells Tec products. Do they have a product (s) that I could use (assuming the tile store sells it in smaller quantities).

3) Is there anything else I am missing (other than grout, any suggestions?)?

4) Does the unglazed porcelain tile need sealing? I believe the specs I have seen show it to be nearly impervious (<0.5% water absorption).

Thanks in advance,
Neil

[Edited by rockford33 on Mon, Sep 28, 2009 at 9:05 pm EST]