Basis sketches to use in Synfire Express ?

No. The Basis Sketch is a simplification for replacing the root container's phrases. You can do that with Synfire directly.

You can turn any sketch into a new arrangement using File >> Convert >> Open As Arrangement from the Sketch editor.

I think that the library is what you are looking for. It is in the manual chapter 10. A sample library is included with the program.

The patterns itself are still there (Playback >> Arpeggios, ...Basic Guitar, ...Basic Piano, ...). To use them you must select one of them and thereafter execute Playback >> Edit Current Sketch. This opens the Sketch (Mixer) window where you can play and edit the sketch. If you then want to have this sketch in an arrangement you can execute the command that supertonic has mentioned (File >> Convert >> Open as arrangement).

In HN2 it were sketches..a band style..like pianotrio, piano +bass ,etc

Yes, they are there. They can be found in the Playback menu. At least in SFPro, but I suspect it's the same in SF Express.

...

How can I play a part of the arrangement 'live' with the pallets ?

Hi
first select the part in time line that you want to play as sketch,
then click to "Container" in main menu and choose "New Container"
now you'll get a new container in the selection area
right click to this new container and choose make snapshot first and then again right click and choose make sketch
...
this is how i work

i hope it helps.

In arrange window, do Container >> Make Sketch