Mark the points.
The arrangement is not your job

By construction rather than by checking. All the labels on a side stand in one column, and all the anchors are on the other side of it — and for points on two sides of a line, the matching that keeps their order is the one that has no crossings in it. So the anchors are sorted along the side and that order is never broken. There is nothing to check afterwards, which is why it holds for fifty callouts as cheaply as for five.

They settle around it, evenly, and their neighbours do not move. The obvious method pushes each label past the one before it, which drags the whole column away from the things it points at; this one finds the nearest arrangement that does not overlap, so a crowded pair spreads around its own middle and a label further down stays exactly where it wanted to be.

Yes. Drag one and the sheet switches to Free with every label frozen where it stood — so the arrangement you were looking at becomes yours and only the one you are dragging moves. The leader still follows.

Yes. An uploaded SVG is placed into the sheet by reference, so none of its coordinates are touched and the exported SVG and PDF still contain the real drawing. A PDF page is drawn to a picture at 300 dpi — turning a PDF page back into vector in a browser means reimplementing a PDF interpreter, and doing that badly would be worse than saying so.

Yes, and it is the reason the tool is built the way it is. Three glue areas get three leader lines and one set of words. Writing the same sentence three times is three chances for it to stop matching.

There is no other way — that is the design. Every figure is a document setting, so a change to the type size or the line weight changes all of them. A sheet with two line weights on it is nearly always a mistake, so the tool does not offer a way to make one.

They write their figures into your sheet and then get out of the way. Every value stays editable — they are six starting points, not six modes, and they are the six conventions this kind of drawing is actually published under.

Where it stops. A dot sits on the thing and needs no clearance; an arrow points at it and stops short. That is the distinction ISO 128 makes — a dot on a surface, an arrow on an edge — and it is why they are two controls and not one with a fill switch.

Outlines for anything going to a press: a text element is a request for whoever opens the file to have the same font, and they will not. Text for a file somebody will edit. The switch is offered for SVG and PDF, which can carry a font; a PNG has no such thing as text, so pictures are always outlined.

Yes. Turn the legend on and the artwork carries only the marks, with the descriptions set in order below it in as many columns as fit. Turn it off and the words stay beside the thing they name. Which is right depends on whether the artwork has room, and only you can judge that.

No. It is decoded, annotated and written back out in your browser. Nothing is sent to a server and nothing is stored. Close the tab and there is nothing left behind.