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Make a list of the content pages that you could write that would be most valuable for your site visitors. Start writing, don't look at DA for six months, do what is valuable for your visitor, create what they want, create what will help convert sales on your site. Do you know that Google does not use DA?   It is a Moz number.  It will not win anything for you. So instead of watching a number that means nothing, spend your time on content that will win your wars.  The more you look at DA the less work you will get done.

Gael, The rule is pretty simple here- there's really no such thing as a "duplicate content penalty" that will hurt your entire site. The question is--do you want those pages with content similar to the original to rank equally to the original page? If so, each page will have to be very unique and build its own expertise, authority and trust (quality content, inbound links, local seo). While there may not be a penalty for content duplicated on your site, google does have a threshold as to what it calls original content and just changing a few words on the page will not meet those requirements. You really should start from scratch and rethink the copy on each page if you're thinking you want these pages to rank well in the future.

Yo, Gael, I don't think any of your ideas are going to work for you. Not only that, but they could hurt your current site, if, in fact that one is ranking. Firstly, it's not about the domain name, it's about the website's relevancy to its target market.  What's that mean? You have to look at your competitors to find that out. What's helping them rank? Where are their links coming from? Are the links coming from Ireland? If so, you're going to need to build  up authority from Ireland. Where it's host could be a factor too. Secondly, your content isn't something you kick around like a an old hackey sack, it's something you grow, nurture and give a permanent home  for, like a puppy. And you don't duplicate it and pass it around to your besties just because they don't have any. You  tell them to make their own--and make it good.  No fluff content is going to rank for you unless there is zero competition. Spinning existing content stopped working more than decade ago. For most small marketers, getting a single site to rank well in a competitive market takes most of their time, let alone three completely different, completely non-networked sites. You might want to start from scratch on these ideas and wrap your arms around some basic SEO principles before you take your next step.