Hosting

Strato offers a bunch of services. If you're renting a VPS, you can definitely join the Fediverse. Just set up a subdomain (masto.yourdomain.nl) and follow the setup guide for any Fediverse service.

If you're renting shared hosting (i.e. a space to dump PHP and HTML files), you may be limited in what you can do. You'll need to pick a Fediverse server that can deal with running in such an environment. Strato does offer a bunch of programming languages (Ruby, Python) but services like Mastodon probably won't be compatible. I think Kbin might actually work, but that depends on the PHP addons and resource limits that Strato enforces. Many of these shared hosts have limits on things like IOPS and inodes, and you may run into that. Performance may also be suboptimal, as many shared hosts limit RAM and CPU time to a level where you can barely run WordPress. Make sure you have plenty of storage, I expect the basic plan with only 20GB of content to fill up quite quickly if you don't disable any caching.

If you don't know what a VPS is or don't know how to handle yourself in a Linux command line, you may be better off renting a specific Fediverse server from a company specialising in that.

Following

Most ActivityPub accounts can follow most other ActivityPub accounts. You can follow a GoToSocial account from your Pixelfed account and boost its posts so your followers on Akkoma and Mastodon can read it, or reply again mentioning your family on Friendica.

Lemmy, Kbin, and a few other Threadiverse services are oriented around subreddit-like communities with votes indicating order, and they're the biggest exception to the rule. Most Fediverse software is built around Twitter/Facebook style timelines rather than topics+replies. You can follow Lemmy communities on Mastodon, but the other way around doesn't work.

As for the apps: you'll need to use the app that fits your server. Many servers offer a Mastodon API, as Mastodon is the most popular ActivityPub server type, but you'll probably have a better experience with the native apps. Lemmy clients don't typically include Mastodon APIs and neither does the opposite work.

The app sporting the best cross-application support I've seen so far is Fedilab (Android app, free on F-Droid), sporting support for Mastodon, Peertube, and Pleroma, and any services exposing those APIs like (I believe) Pixelfed.

In theory, apps could use the ActivityPub C2S standard to interact with ActivityPub servers of any type, but in practice that API isn't implemented, as it's not very well-defined and ignores the reality that most ActivityPub servers are made with a certain bias (like "optimised for timeline", "optimised for sorting based on votes"). I do hope C2S becomes more popular in the future but for now it's kind of theoretical more than anything.

Viewing a Lemmy account's posts from Mastodon seems to work. Going the other way, viewing a Mastodon account's toots from Lemmy, does not work.

Pixelfed can see Lemmy and Mastodon accounts, but it does not show the posts or comments from those accounts. The reverse is also true: Lemmy and Mastodon can see Pixelfed accounts but not their content.

At least these were my results the last time I experimented with cross-platform interaction. Maybe there are some tricks I have not learned yet.

For the second, you cant follow accounts on lemmy but you can follow lemmy accounts from mastodon. (it will show both posts and comments the person makes as boosts)

Same for posting, you cant post so it shows up on mastodon since lemmy doesnt have hashtags but you can post and comment from mastodon (post by mentioning the community in the post and comment by replying to a post made on lemmy). Note on posting from lemmy to mastodon though is if you have a mastodon account that follows the lemmy account and comments on posts with hashtags that comment and the parent post will appear in those hashtag feeds, just looks spammy

is it possible to start an account on this instance that can be followed via either Mastodon or Pixelfed

I just looked up your Lemmy profile in my Mastodon app and it looks like I can follow you at least. There's no visible post history though, so that might be a blank?

and vice versa

I'm not aware of any user follow feature in Lemmy? It's all centred around community subscriptions AFAIK. That doesn't mean it isn't technically possible — it's the same protocol as Mastodon etc — but if there is no UI option to follow each other, the question is sort of moot.

Not amateurish at all, but good questions. I’m not confident enough to answer your second question, but on your first question: yes, you can use the hosting service you already have. Given that you are renting a VPS that is. It looks like Strato is calling this “hosting”. Don’t use their “WordPress hosting” package for this though, as it won’t allow you to install the instance software.