how to adjust # of ticks on Bokeh axis (labels are overlapping on small figures)

You can control the number of ticks now with desired_num_ticks property. Look at the example from the bokeh docs (and this issue).

For example, in your case, something like this: plot.yaxis[0].ticker.desired_num_ticks = 10.

Looks like there is still no direct way to specify this. Please follow the related issue. This is a workaround:

from bokeh.models import SingleIntervalTicker, LinearAxis

plot = bp.figure(plot_width=800, plot_height=200, x_axis_type=None)
ticker = SingleIntervalTicker(interval=5, num_minor_ticks=10)
xaxis = LinearAxis(ticker=ticker)
plot.add_layout(xaxis, 'below')

You can control the number of tickets via the interval parameter in SingleIntervalTicker.