1) Yes, see the brush dynamics. You likely want one that relates pressure to size (or to opacity+size). There is none by default but you can look at the one that relates pressure to opacity. Note that the standard ones are read-only, you have to make a copy to edit it.
2) Edit>Preferences>Tool options>Paint options shared between tools
3) You can set you own defaults. But in the long run you will find that the current default is better
2) Edit>Preferences>Tool options>Paint options shared between tools
3) You can set you own defaults. But in the long run you will find that the current default is better