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JPGs can be given any colour space but can only be 8 bits per colour channel. Some printers can handle more than sRGB and more than 8 bits per channel.
Exporting applies its own sharpening. You may want to minimize that sharpening and apply your own but perhaps it does not matter much if you have already correctly sharpened the master image file in Lr with the necessary capture sharpening. I don't know the ins and outs of how Lr works out what sharpening to apply to exported files for printing or display.
Colour space is important, as is the colour space info being put in the file. I don't know how Lr handles that. If the range of colour channel values in a jpg file is 0 to 255 and there is no info about what those numbers actually represent then you can easily get the wrong results in the prints. A printer may assume sRGB but if Lr was using ProPhoto or Adobe RGB then it will not look like sRGB should.
Whatever colour space is used you can assume that the printing mob will adapt your image file to suit their own printer profile and give you what you thought you would get. Alternatively, you can find out what printer profile they use and do your own print previews using that profile so that you can edit colours accordingly - but don't bother unless you expect that their printer cannot handle the colour range within your image, and that your image needs to be tweaked.