This questions are not software or OS specific and professional printing services offer at least some guidelines. E.g. Bay Photo lab: File size & Preparation
The services I've checked recommend 80-120 cd/m² for monitor brightness. Economy printing services expect your images in JPG (sRGB). They don't read the embedded profiles. Other profiles than sRGB create unpredictable results. Professional services take care on embedded color profiles and except sRGB or sometimes AdobeRGB.
Out of gamut colors could be desaturated, although I never did that. Comparing a print and playing around in darktable with desaturation gave me similar colors.
Your colors most likely get desaturated. There is a risk of unsightly color blotches.
"sRGB" or if your screen supports it and your service accepts it then "AdobeRGB". I stay with sRGB as it's bullet proof.
You could/should turn of automatic correction during the ordering process, if you want to see your image development. Or at least the direction, because I don't feel that I've full control over the results. It's a bit of trial and error.
I guess with a laptop screen it is even harder to get what you want?