But now that it's running, I have 2 questions. Is there a way to make it full screen or at least bigger?
The play has a fixed resolution, you cannot change that. You can change the screen resolution of BasiliskII, but that won't change the resolution of the game. You can set the screen resolution in MacOSX to lower values. That will make everything on your screen look larger but (on a LCD screen) less sharp.
If your Mac is a Intel Mac, you could try the "full screen capable build" of BasiliskII (see sticky topic in BasiliskII forum). That build can run the emulator full screen.
When BasiliskII runs fullscreen, the game will still be at the same resolution, but everything around it on your screen will look black like now only in the BasiliskII window.
To run that build full screen, set in GUI Video Type to "Fullscreen" and Width an Height to "Maximum".
If you set Video Type to "Fullscreen" and Width and Height to 800 and 600, you may get as close to what you what as possible.
(Don't try to run the UB build of BasiliskII that you are now using, it will result in a black screen only.)
And I'm not entirely sure and could be wrong, but it seems like the game is running a tad bit slow. It's not really that noticeable and may not even be lagging as I am paranoidly thinking it is, but it might be so is there a way to fix this?
In the GUI, set the Window Refresh Rate to "Dynamic" and enable JIT Compiler for best possible performance.