...Its a pretty good do-it-all bike when paired with wide, fast rolling tires...

I'm intrigued by your rack, where did you find it ?

I tried some Cooma pink pads...

Me too and for a year or two. Not sure if they changed something, but they are not as good as they were.
I ride the orange(ceramic) ones from this shop now https://kingstop.aliexpress.com/store/233959

They have a great grip and are silent compared to the Cooma pink that were already kind of silent.
Not sure, I have the impression they wear a little faster, but give a better brake feel. I moved all my bikes to them.

Last year it was raining so much in Belgium I decided to invest in rain jackets.
And scouted the shops to find some bargained jackets and found one light Pearl Izumi, and two Vega Extreme and Absolute from Santini all flashy and based on the Neoshell fabric.
At around 100€ each, it was expensive in total, but it gave me the joy back of riding in extreme weather.
Together with AGU Foul Weather shoe cover I was able to make something out of that shitty season.

I bought one from this shop 6 years ago: https://www.aliexpress.com/store/2817078

I thought I would need a big one, so I took the 30L but it wasn't a good idea after all.
Except that a 52 eagle cassette fits in, I have no usage of so much volume generally and it is too big to warm.
So I put now my stuff in glasses, or plastic bags with hot water and cleaner.

...Could you help me figure out which size would be a better fit? Thanks in advance!

You can do some homework 
Take a bike you ride and compare it with the 707 here https://geometrygeeks.bike/bike/carbonda-cfr-707-2023/

You will quickly see if a long stem will do the trick, and how many spacers you will have to add compared to your current bike.
If you don't have a bike yet, ask a friend so you can compare to something you actually did ride.

Looking for blips online, i think i read that you can change chainrings by clicking both blips at the same time.
Seatpost isn't on my radar but i think i read that it doesnt work with blips.

That was the status a few months ago, yes. I’m wondering if there have been any updates since then because it’s unclear to me why a double ring setup would work while the seatpost doesn’t.

Is the 505SL still available? I can not find it on their page?
How much did you pay for it?

Contact them by email, it is definitely available and the new version is a great frame to build and ride.

You need only the AXS RD, Wireless Blips, and a 12-speed cassette with a matching chain. The latest AXS firmware no longer requires levers or a blip box... Also, the force and red chains last a long time and are worth the cost.

Do you know if the recent firmware allows the wireless blips alone to be used in a 2x setup ?
Or paired to an AXS seatpost ?