https://c.im has 5000 characters limit.
https://kolektiva.social (anarchist) has 10 000
https://infosec.exchange has 11 000 characters and formatting.
https://qoto.org has 65 535 character limit and other features, but some servers (including Universeodon and main British one - mastodonapp.uk) block it.

You can still decide to transfer your account later on, so starting on mastodon.social isn’t too bad. https://guide.toot.as/guide/move-mastodon-server/#1-guide-configuration Even if i would suggest to change it, as it kind of beat the decentralization aspect to it, i believe ~80℅ users are just on this default instance. The official website has it’s own list of suggested servers per interests and some rules here : https://joinmastodon.org/servers You can search via a minimum maximum character limit here : https://mastodon.help/instances/en

By default, Mastodon servers can access all other servers. It’s just the admin who can decide to block other instances on a blacklist for all the users on the instance they use. You can also just block yourself instances or users if you want. As long you don’t take a political, shitposting, or fascist one which are often blocked on a lot of instances.

I tried to find one that kind of aligned with my interest and didn’t have a crazy number of users like mastodon.social. Reading online about picking instances, the recommendation to pick a smaller instance came up numerous times.

Went with sunny.garden since it’s a creative/artsy/tech instance and it’s been great. My local feed moves at a decent pace with content I enjoy, but I could also see mostly everything else on the federated tab.

host your own if you care about privacy

I’d say go for mastodon.social, you can always move if you later find one you like more.