Knluk no problem, I imagine you would have found the best grind setting before but the high temperature made it taste too bitter. It’s easily done.
Because of its design that minimises the contact (and heat transfer) from basket to portafilter, the Robot doesn’t drop temperature so quickly like the Flair. Off the boil water into the basket usually results in a starting brew temp of round 90c-ish so for your beans I would aim to lower the basket temp down gradually towards a minimum floor of 85c to see how that tastes.
Yes I usually find that filling the basket with water to around 1cm from top works fine. You can leave slightly less space at the top you just run the risk of spilling hot water when you lock it in. I can’t imagine this will affect taste dramatically unless you do what Hoffman did in his review and underfill it too far as that could make it harder to generate pressure.
You’ll soon get a feel for the pressure and it comes more naturally now you have an idea of the correct range. As CoyoteOldMan mentioned usually you build up to pressure quite quickly then you slowly decline towards the end of the shot, so don’t worry about sustaining the max pressure for any period of time. I usually go off the feel and flow from the basket and adjust accordingly but it took time and plenty of bad shots!
Once you dial in a few different roasts you’ll also end up defaulting to different starting parameters depending on your preferences, but I’d say aim for a 1:2 ratio for dark roasts and nearer 1:2.25 for medium ones (lowering the dose and raising the ratio and water temp for even lighter beans since they’re harder to extract). As mentioned the important thing is to keep your starting temperature, ratio and preinfusion consistent as you dial in the grind. Then tweak them one at a time to perfect the taste in cup.
Lastly don’t beat yourself up for a bad cup, just write down notes that you might find useful for next time so you can improve with the next attempt. Your shots look a lot better than what my early shots were like. Good luck!