of reading
3576
Read books
mahouka koukou no rettousei - there is alot of magic there and even way to use tech to assist in magic and even if he make a manga there are many way to use magic to make it lpok different than the manga, or say magic is the same everywhere
shaman king, the power system from that world can even be learn by normal people after long term contact with spirits
Dont worry i like your story, try to add a recycle funtion, to his system for thing he doesnt want but the output is less than whar he put
Will he get a funtion for the system like temporar summon in exchange for something and he can chose 1 out of 5 options for a temporar help.
If he is strong enough he can go to a world like hunter x hunter to learn nen or mahouka koukou no rettousei, in that world they use tech to assisst in magic which can be useful to get more in magic and tech, also in hunter x hunter be honest with the president nero might be faster be telling him you are not from this world and exchange few things, he might be even be will to travel to another world just for the fun of fighting someone strpnger than him, and you get a good nen teacher and friend
If you need ideas just create a grupe or something so to ask for some ideas, some people do that and also for opinions
"Hughes" from, fullmetal alchemist brotherhood, summon him
Dont give him something to strong to early, or it wont be fun, give the maid something good to help him, and summon "spike" anf "L" from cowboy bebop, and death note...
Next time he need to use the "domain expande" he can try to throw the enemy as hight as posible in the air to avoid hurt anyone else, unless he get another domain...
abe no seimei, template from the anime "onmyoji" (netflix) ... onmyoji are mages, Exorcist, and fortune teller... and when it camo to fight demons that will be useful and they know magic.