Copper pour heatsink question: soldermask / thermal vias.

I have a couple of question regarding copper pour heatsinks. I want to use a D2PAK/TO263 linear voltage regulator in a project I'm workin on. I am going to make the thermal pad about 1 in^2, and was wondering what to do with the solder mask. Should any solder mask be applied over the copper pour? On one hand I would immagine the solder mask would insulate the heatsink which would be undesirable. On the other hand, I can see tremendous difficulty when soldering the thermal pad on the D2pak to the copper plane if ther was no solder mask. Would the solder not just wick away from the pad and disperse evenly over the entire pour? I plan on assembling this board using a toaster oven, but if I had to hand solder the thermal pad with a solderin iron, it seems like it would be very difficult.

My second question is whether or not to use thermal vias. The board will be a 2 layer board, with a copper pour on the bottom layer attatched to GND (the voltage regulator is on top). Where should the vias be placed? directly under the voltage reg? around the outside of the voltage reg? would they not also act as a sink for the solder, drawing it away from the voltage regulator. Let me know if this isnt clear...

Also the voltage regulator's middle pin is of course connected to gnd. does the large pad also need to be connected to GND to work properly electrically? This would kind of make the thermal vias kill 2 birds with one stone.

Thanks in advance,
-Liam

Myself I would have the solder resist apertures only where the pads are of the device, the rest of the copper does not need to be visible.
The interconnection vias should not be underneath the device as that removes copper land needed to absorb the heat from the device, however you can put lots of them in the surrounding copper.

Yes if the big pad is connected to ground internally then connect the pad to ground in your circuit, it will help provide the device a better ground.

Re: Copper pour heatsink question: soldermask / thermal vias

Solderresist do not stop distribution of heating. If dielectrica did that You would not be able to use lower GND layers effectively enought.

Stop the soldermask 0.1 mm from pad, that works perfectly in addition, repeat the pour at layers below and "connect" with small vias.