It sounds like Hamy is getting the best possible care. The biggest issue we encounter with captive squirrels is diet. I see CC already sent you the link for a healthy diet. I am not familiar with the rodent block you have listed. I know the cost of Henry’s blocks and shipping to the UK is cost prohibitive, if they even ship there. There are other rodent blocks that should be available via Amazon. One of the best blocks is Envigo Harlan Teklad 2018 or 2014. Other good blocks are Oxbow Regal Rat, Mazuri Rat and Mouse Diet and Zupreem Monkey Biscuits. All of these are a hard extruded block and not a seed mixture. You DO NOT want a seed mixture.
Please be aware that as Hamy matures he may become aggressive and want released. The fact that you are handling him as much as you are is a good thing and may help when this time comes.
We are here to help you along the way. One thing you should have on hand is some type of human antibiotics. It’s best to have them on hand and not have to scramble to find them if the need ever arises. Some of the antibiotics that are routinely used with squirrels are: Clavamox (animal)/Augmentin (human), Baytril (animal)/ Enrofloxacin (human), SMZ/TMP (human), Doxycycline (human). If you ever have a need to treat Hamy with an antibiotic just start a thread on here and post what’s wrong, the drug and strength you have and Hamy’s weight and someone will be able to tell you how and the amount to dose.
Best of luck! We love pictures.