Congrats on new Cremina. That flush is OK. I do not use stock basket but I think with it the max is 14 grams. So go for about 14. If you use 14 grams and tamp then lock in portafilter and take it out without pulling the shot if puck is not damaged you are OK.
Get Elektra Leva
double-basket which will allow you to dose up to 16-17 grams depending on coffee.
I find sweet spot with the Elektra basket is 15 grams.
Get the OE
temp strip which will make it much easier for you to know when group head is at right temperature. When first bar on the strip is deep blue temp is right and you can pull your shot. This is in my opinion crucial for consistent excellent shots with Cremina.
When raising the lever make sure you do it slowly since you are pulling air through the puck and doing this hastily will break your puck and cause massive channeling.
With regards to pull on the lever and grind, if you are pulling on the lever and are tipping machine, you are pulling to hard and grind is too fine, grind coarser. Pull should feel almost like knife through cold butter.
Once you have your grind and temperature sorted out you should be getting good shots.
Good luck.