Icons format and Actions/Hint text?

What are icons usable format(s) in Glide ? and which free provider would you recommend ?
Up to now I did cut&paste of emoji using from https://emojipedia.org/symbols/
Do you know other references ? Is there a possibility to create and import icons in Glide ?
Shall we use SVG (vectoriel) format ? How to import them ?

For the Actions like the ones linked to OK button, Form, Add, Edit, Remove, … is there possibility to customize the pop-up messages “Add”, “Submission”, … including “+”, “EDIT”, “DELETE” and related icons … with the PRO version ?

For the Hint text (placeholder) is there a possibility to define 1 text by default (in DATA view) instead to have to define it manually for each entry component ?