Gen up on your maths, big style. That's the biggest difference for you in terms of knowledge. You think you know place value but you really don't. Be prepared to REALLY know your grammar. And I mean, REALLY. Be prepared to APP and go up a sub level at a whim. As for creativity, that is for your TA. You are there, in primary, to get them working in English and Maths. Be under no illusion. Be prepared to squash the foundation subjects into 1 hour in the afternoon. History will make you weep.
The lightbulb moments are there, but no more than they were in secondary in my experience, and I taught History at secondary for 9 years before swapping. The same problems exist: the relentless push for targets. In primary, the middle "doing ok" are happily left alone, whereas the HA and LA are pushed more because they are the ones whose stats matter. That's the biggest difference in terms of attainment, where we were used to pushing D's to C's.
Personally, I have found it to be much more pressured, rather than less, with a MUCH heavier marking load and a far heavier SEN prescence and EBD prescence in the classroom, with less support from SMT. All the real EBD and SEN has been weeded before it gets to primary. In primary they are in your classroom all day.
I would organise. Label all drawers, makea filing system, a big book corner. Order your cupboard to have an English, Maths, SPAG and Foundation area and spend ages sourcing stuff. You are used to a department cupboard: most primaries don't have them. Your resources are YOUR resources, and unless the staff want to, they don't share. You could end up going in with nothing to teach from. Look for short, medium and long-term plans and see what they have. If they don't have, panic, that's not good.
Secondaries have SOW and so on, primaries, not so much. You could end up regretting the moan that everything is planned for you. When you plan a PE lesson, you'll see why, or end up planning a keyboard lesson from scratch!
I have found it to be more or less equivalent in terms of job "joy", "wow" moments, and much higher in frustrations and lack of resources. And levels in Secondary were bad enough, wait till you hit primary, where we talk in terms of teeny bits of sub level.
I'm not trying to put you off, but really, prepare, prepare,prepare! It really is VERY different, and to my mind, harder in terms of marking. Alright, 30 X As plus 30 X A2 plus GCSE class every weekend takes time, but 30 English, 30 maths plus 30 topic every night, plus Big Writes, Progress Writes and APP takes longer, and there is no down time in the Summer when your classes leave. And nowhere near as much protected PPA, unfortunately.
Pluses? No moving classrooms, you get to know the class really well. You get to do art and read stories. You do assemblies with costumes again. The kids tell you bizarre things and you do have a laugh with them.
Of course, this varies from school to school. But speaking to others who have made the swap, it's pretty similar complaints.
I wish I had swapped prepared with a folder of maths / english sheets, and powerpoints. Do that, from the medium term plan, if nothing else before you get there, so you get a chance to adapt things rather than write them from scratch.
Long, sorry!