> - How will I be able to operate my small company website in the future in a legally compliant manner?
What exactly worries you here? If you could be more specific I'd be happy to try and answer your questions.
> - How exactly does a privacy policy have to be worded
The GDPR provides a list with the information that you need to provide to a subject when processing his/her data (also look at the other articles of the same section):
https://gdpr.dpkit.com/gdpr/chapter-iii/section-2/article-13...
I think a simple text with clearly stated information is sufficient and I don't think that you'll get sued if you ensure that the information is accurate and complete, which shouldn't be too difficult for small websites.
> - In which way will I still be able to store data for contacting my existing B2B customers (such as email addresses and phone numbers)?
In a nutshell, you will need either their consent or a legitimate interest (as you do now as well): https://gdpr.dpkit.com/gdpr/chapter-ii/article-6.html
Communicating with your existing business partners (e.g. to inform them about new products or ask them for feedback) is a legitimate interest so you can still contact them without asking for permission first. They can tell you to not contact them again though (which isn't really new either).
> - Will I still be able to use anti-spam and security plugins for my website?
Yes, spam protection and security are legitimate interests and even required to comply with the GDPR (reasonable technical and organizational measures), so you are allowed to process and store IP addresses for that as long as the processing is commensurate (i.e. you should store the addresses for a limited amount of time and delete them as soon as you don't need them anymore). Here the GDPR is very similar to the BDSG as well in the sense that it allows processing of personal data if there's a legitimate interest, and ensuring the security and integrity of your service is a highly legitimate interest that can override many of the normal restrictions imposed by the legislation.
Hope this clarifies some things, would be happy to hear about your other concerns / questions as well!