If my target audience is situated mostly in a certain country (about 60%), is it a really huge difference whether a website has local domain name (i.e xxxx.co.uk) or international domain name xxxxx.com? Is it worth to buy local domain for those 60% but sacrifice other 40% or is it fine to stay with .com? And similar question: is there any difference where my host server is located for Google rank for different countries?
if the domain is available then register both and you can use cctld to brand in local area and .com as main site google ranking affects wrt various countries too you may be in first position in google.co.uk but it may be in second page of google.com
I would go with .co.uk, but also register your .com name so you can protect your brand, Yes there is difference, i recommend you to host your website in your country, e.g. in UK if your business is based in UK
Your physical server location also effects your google positioning! If you have a server in the UK for example, you would be more likely to rank higher in the UK version of google search and what not.