Logic Masters Deutschland e.V.

It's almost my birthday!
So I made this thematic puzzle, which is the first time I've really tried to stick to a theme across the entire puzzle (that is, the outside clues). I have made a CtC tribute puzzle, but that only had the theme shapes on the left.
See if you can guess my age and the date ;)

Rules:

Normal sudoku rules apply.
Outside clues are either X-sums clues or Next X-Sums clues.
Figuring out which is which is part of the puzzle.
When there are clues on both ends of a row or column, one of them is an
X-Sums clue and the other one is a Next X-Sums clue.

X-Sums clues indicate the sum of the first X digits starting from the first cell in the corresponding direction, where X is the digit placed in the first cell in that direction.

Next X-Sums clues indicate the sum of the first X digits starting from the second cell in the corresponding direction, where X is the digit placed in the first cell in that direction.

Example: if r1c1 was a 5, then either r1c1 through to r5c1 would add up to 21, or r2c1 through to r6c1 would add up to 21.

Try the puzzle here. Have fun!

Comment and ratings are as always highly appreciated!