My experience with large format plotters is mainly from a CAD perspective rather than graphic design, but in terms of technical capabilities the two are generally the same.
Most large format plotters have similar inkjet technology to that used in everyday inkjet printers, the main difference (aside from cost!) is the ability to handle large paper. So as a general rule, anything that prints ok at a particular scale on an A4 sized domestic printer will be ok on a large format device at the same scale. For CAD work we generally used 2.5mm as a minimum character height, which I think roughly equates to 7pt. Smaller sizes could be used with clearly readable text, but comfort and ease of reading were limiting factors.
The main issue is the software and the settings used. It is important to understand the difference between raster and vector graphics, so if you don't I would google the terms and understanding how your final chart will be produced. Although the differences between raster and vector become more important if you scale up objects (such as text), it is also relevant with small details, and critical if the process of printing your chart will involve conversion from one to another.
Also be aware that one of the limiting factors in large format plotting is the memory available on the plotting device. Although this is less of a concern on modern equipment, older devices may struggle with a large high-resolution raster image.
You need to make sure the printshop understands that although the sheet will be large, the detailed information is important to you. Some printshops may be more used to printing large posters and enlarged photos, intended to be viewed from a distance. For these the print quality is actually not as important as it is for your charts.
Another possible consideration is the amount of ink used to print a full-coverage A0 sheet. The graphic you attached to your post has an attractive yellow background, but depending on the printshop you use this may cause problems or additional expense. Some printshops will have a standard charge based on the size of print (e.g. A0). But others may charge differently depending on whether it is a full-coverage print (e.g. enlarged photo) or CAD type drawing with partial-coverage. If the one you use offers this option then you might want to consider removing the yellow background if the printshop agrees the result is eligible for the lower cost option. For example one randomly selected company found online charges £11 for an A0 'plan' print against £19 for an A0 'poster' (although the latter is also on thicker paper).
Finally, in my experience it is best to avoid gloss or semi-gloss papers for printing text at small sizes. Some of the best results come from using 90g plain paper. If possible, ask the printshop to show you samples of text printed on their different paper options.
