Reactions can be as simple as a "+" message which most clients read as a 'like', clients also choose to use other reactions (damus on iOS defaults to 🤙), try out the other clients too 🥳
Profile pictures can be hotlinks to images. All sorts of extensions work, even animated GIFs! Use a public image host or host your own
Consider setting up your lnurl/lightning address and you can get zapped âš¡ too!
Use hashtags as you would on other apps