If you mean window.open then the details can be found here.
Be aware of the problems with opening new windows especially resized ones that are likely to be blocked by adblockers etc (ignoring accessibility concerns for now). Read the MDN article for full details and other issues.
Yes its an age old debate but I still prefer to leave it to my users to decide. There are exceptions of course but they need to be managed correctly.
However, I think that authors should be able to make their own choice once they've read the pros and cons and decide on what's right for them. There 'never ever' is a one size that fits all but a list of pros and cons and you have to weigh them up and decide on the best course of action for the task concerned.
Sounds like it may be better to open a modal on the same page perhaps or if all 260 link destinations are on another single page then why not include the navigation on that page to start with and just keep users on the same page? e.g. Similar to how the W3C does it with their long list of links here (i.e. links on the left and content in the main panel on the right).
Obviously if your 250 links are links to 250 different pages of your site then I might suggest some better sort of navigation might be required especially if each page is heavy with images and content.