I can't answer the question about the thermal characteristics as I am not sure whether Multisim takes this into account or not. If it does it would have to be done through the simulator setting as I do not believe the model has anything concerning thermal characteristics that I was able to see.
The question I can answer is the one about the footprint. If your version supports it then you can go down to the spreadsheet to where it says "Components" and scroll to the right where it says "Footprint" and click on the box for the particular component. This will pop a dialog box up and from there you would click Select from Database and from there you can find the footprint you wish to use with that component.
If your version doesn't support the spreadsheet method you can do the same thing by right clicking the component and then select Properties and from there select Edit Footprint. Then click Select from Database.
I hope this helps some.
