Do you have any recommendations which optics kits to get and where to get them (preferably available to the EU)? What about a good budget entry eyepiece?
I'd recommend a quality 20/25mm plossl rather than the gold/red line 15/20mm that display a lot of issues.
For better eyepieces, at f/5, the rubber-top generic eyepieces with color bands sometimes branded as "artesky" are great for their prices too.
If you have a bit more budget, Explore Scientific is generally the overall best quality/price ratio. Avoid baader hyperions, except for the 13mm which hits above its price (second-hand)
The 6" f/5 optics kit are a bit of an oddity, those we test with our interferometers are consistently good, whereas smaller or bigger diameters are subject to a lot more vatiations.
Or better : attend a few nights at a nearby astronomy club, that will allow you to get a feel of the practice, what you can see, what you should expect...
Depending on your location (city? middle of nowhere?) and willingness to drive to darker skies some types of instruments and targets are better than others.
This kind of kit is focused on being compact and lightweight, but that can be an advantage or a non-goal depending on what you want to do.