Plotting points in base R maps

Question

this might be a long shot as I am unable to provide all the relevant data, but maybe there are some general tips on how to solve the following problems:

There are three things I want to resolve:

1. I have overlapping points in my plot, where the first line of the points command are the base points that are shown in open circles. The second line of the points command show the filled circles. Unfortunately, some overlapping between points occur at the some locations. How can I make sure that open circles won't show, if there are filled circles on the same location? Thus I give preference to show filled cirlces over the open ones.

2. I made a frame, where my plot is visible within the settings of that frame. But I want to zoom in more on the plotted data. So the grey area on the right, and the white area on the left are not relevant. I think I should be able to adjust this in the first line of the plot command, but adjusting these coordinates was unsuccesful so far.

3. lastly, I want to fit in the legend into the plot and place it in a better position. What are some handy commands to manipulate legends in base r plotting?

[![Map with points][1]][1]

Code I used:

plot(gadm2, col = "grey", xlim=c(4.9,5.9), ylim=c(52.25,53.1), main="Forage 2021")
plot(gadm,  col = "white", add = T)
box(which = "plot", lty="solid")
axis(1, at=c(5, 5.5, 6), labels=c("5°E","5°5 E","6° E"))
axis(2, at=c(52.25, 52.5, 52.75, 53), labels=c("52°25 N","52.5°N","52°75 N","53° N"))
points(All_Receivers$Longitude, All_Receivers$Latitude, pch=1, cex = 2)
points(brplot$Longitude, brplot$Latitude, pch=16, col=brplot$Color, cex= brplot$group/1.5)
legend(5.75, 53.10, legend = c("1", "2-5","6-10",">10"), title="Number of bream", cex = 0.7, pch=16, pt.cex = c(1,2,3,4)/1, y.intersp = 0.8)


  [1]: https://i.stack.imgur.com/KT3vK.png