Have you ever let it run on an auction domain that has already traffic

?
Using it on an auction / expired domain will be a good idea. Just make sure that the domain is not spammed in the past and is clean.
I am planning on scraping articles from English websites with WP automatic and after let them go through DeepL to auto post them on my Dutch site.
Has any of you guys have experience with this? Will they rank

?
I am using wp automatic for couple of my auto pilot websites. It is by far the best auto blogging plugin I have found in the market (given the features it offers and the cost of only $39 ). So you should definitely go with this plugin.
Idea of translating the content to your native language is also good and I think you should certainly try it.
I have a few words of caution for you -
1) Do not consider that this autoblogging project will run on 100% autopilot. Even aeroplanes don't fly on auto pilot completely. They need humans to make sure they are running smooth. Same is the case with website and blogs. You have to constantly keep monitoring and checking if all the systems are working fine and there are no glitches and hiccups, etc.
2) Autoblogging plugins only speed up your content creation process, they will never solve it. You will have to constantly monitor what is being imported and filter out the raw code, wrong words, poor content, etc.
3) In any case you will have to invest on the SEO just like you would on any other site. Auto-blogging is not a money minting machine that works on its own. Keep building good quality backlinks on a regular basis. This is a key. If you stop building backlinks, your sites will stop to grow beyond a limit.
4) Using a good translator like DeepL is the best solution. You have selected DeepL which is absolutely fine.
5) last but the most important thing -
People will always share their experiences but you have to do it yourself once to see if it works for you or not. So be prepared for that. This is how I work.
Any more questions? Feel free to ask.
Cheers!