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25% is a good amount.
You can do it manually its just as easy. I used the mosaic tool on my last mosaic (yet to be processed - warning they are time consuming).
But I went for 20-25% overlap as you want plenty for good stitching points. Too little and there are not enough stitching points for a good combine.
The main advantage of the Sky X tool is speed. You click on the panel and it go-tos the centre of the panel. Nice and fast but you would still be wise to double check it by using the focus image against your last panel's luminance image (reduce it so its the same size) and manually line it up if necessary.
Automation is good but it does not replace your need to control things.
With mosaics its best to image the same time of night for each panel, the same exposure lengths, the focus is critical so make sure its spot on for each panel (one panel with poor focus stands out). Usually the problem with mosaics is the background's are different, hence the previous statement. Overlap 25%, about 2.5 hours per panel, under the same circumstances. You'll find that is hard by itself as one night is clear the next may have high thin cloud causing halos, or wind causing guide errors. You end up with some incomplete panels that need to be imaged to complete them on a different night. So keep good admin, do a manual drawing where each panel goes (some panels in a multi mosaic can be undistinctive and hard to work out were they go so number them like Sky X does and save them that way).
Best to do a 2 panel one and see how you go. If successful do a 4 panel one. I wouldn't try an 6 or 8 panel one to start.
I notice Rogelio often uses 2x2 binning to reduce exposure times at the expense of resolution but when viewed at regular sizes the resolution is fine because its such a wide field of view. He goes 1.5 hours per panel which is low but then he'll do a 16 panel mosaic and he uses Pix Insight which is a difficult program to use.
Greg.
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