So is it probably safe to plug it in now? Any seals or gaskets dry out after all this time?
If you have not used a dish washer, do you know how to install it and operate it?
Believe me or not, that is not a trivial task. RTFM, at least.
As for installation procedure, not sure if all dishwashers are the same..
You must know that the built-in (is it the correct white-goods term? "Embedded" maybe?) models
do not have proper chasis and counterweigh as free standing models do! These heavily (pun intended) rely on the surrounding equipment/furniture.
First you should check if it is properly aligned. These types are much lighter but if you try to pull out filled baskets, it would tip over and ruin your day if not firmly installed. Also check if the locking mechanism/front door is not skewed. If it is then it may happen it would flip the locking lever and you won't be able to close the door.
Next, I'd check if the water supply valve cuts off correctly. Such failure might be very expensive.
Then there is a water hardness adjustment. You need to know how hard your tap water is. This is not critical but for best performance you have to provide adequate quantity of both softening salt (cheap) and detergent (expensive). Otherwise you would have to put much more detergent for same performance. In my dishwasher the adjustment is one-time only, you cannot readjust it as it relies on cutting off a plastic pipe so take your time with that.
With water outlet - if it ever happens the pipe is damaged or falls below the tub level.. Same story as with washing machine.
That would be all for the successful installation.