Custom labels in a pie chart

Question

Using @kglr's approach (see here) we can create the following pie chart

coloring = Thread[{-1, -2, 0, 1, 2, 9} -> {Yellow, Purple, Green, Blue, Red, Cyan}];
data = {0, 0, -1, 1, 1, 2, 9, -2, 2, 1, 1, 1, 0, 0, 9, 9, -1, 0, 9, 2};
ca = ConstantArray[1, Length@data];

positions = {5, 13, 17};
labels = {"label5", "label13", "label17"};

ca[[positions]] = MapThread[Labeled[#, #2, "RadialCallout"] &, {ca[[positions]], labels}];

plot = PieChart[ca, SectorOrigin -> {{\[Pi]/2, "Clockwise"}, 0}, 
       ChartStyle -> (data /. coloring), ChartBaseStyle -> EdgeForm[White]]

My main question: is there a way to explicitly define the size and fonts of the text labels? Perhaps adding LabelStyle -> {14, Bold, Blue}] My secondary question: in my actual data file, there are cases in which the labels are too close and the corresponding text is overlapping (see the example below). Can we do something about it?

EDIT

Using @kglr's solution I get the following

As we can see, the borders of the frame are overlapping each other.

Answer 1

I learned from this answer by rcollyer that we can use Callout with PieChart in versions 11.1+.

coloring = Thread[{-1, -2, 0, 1, 2, 9} -> {Yellow, Purple, Green, Blue, Red, Cyan}];

SeedRandom[123]
data = RandomChoice[{-1, -2, 0, 1, 2, 9}, 200];
ca = ConstantArray[1, Length @ data];

Some positions and associated labels:

positions = {1, 2, 3, 40, 170, 171, 172, 173};
labels = Style[#, 16] & /@ {"label1", "label2", "label3", "label40", 
    "label170", "label171", "label172", "label173"};

Wrap 1s in positions in ca with Callout using associated labels as callout label and style each label based on corresponding part of data:

ca[[positions]] = MapThread[Callout[#, Style[#2, #3], Appearance -> {"Line"}] &, 
   {ca[[positions]], labels, data[[positions]] /. coloring}];

Place the epilog inside the to avoid overlaps with the sector labels:

plot = PieChart[ca, SectorOrigin -> {{π/2, "Clockwise"}, 1}, 
  ChartStyle -> (data /. coloring), ChartBaseStyle -> EdgeForm[White],
  ImageSize -> Large, 
  Epilog -> {Line[{{0, 1}, {0, .8}}], Arrowheads[Medium], 
    Arrow[.9 {Cos@#, Sin@#} & /@ Subdivide[π/2, π/6, 10]]}]

Use Style[Framed@#, 16] & when defining labels and add the option ImagePadding -> 20 in PieChart to get