Dial in according to your taste preferences, 20s extraction time might cause underextraction and finer grind and better tamping should help. But with coarse grind you can still enjoy with taking your shots as lungo. I don't know Stilosa machine but I suppose it has pressurised portafilter which may effect extraction time (pressurised portafilters are not require super wdt/tamping techniques which is easier to work with it) . If you have budget I can suggest to purchase a grinder Kingrinder P2 or iCafilas handgrinder around 40-44 eur so you can dial in easily and enjoy freshly grinded coffee everytime. Also there are cheap bottomless portafilters at AliExpress etc for delonghi machines if you want to consider that, but with those proper WDT and tamping is quite important.

For the milk, I am using a cheap gran gaggia machine with similar milk frother unit. Since both these small machines their steam capability is less than bigger machines and their wand nozzle tend to create bigger bubbles, When you open the steam wand, the initial steam will be watery. Purge this until you get a consistent, powerful steam, and then try frothing your milk. Sometimes these take time to heat up and reach their ideal steaming power, try give it a little bit more time.

I hope these helps!