Alloy:
Does the Search function search tags.
Can you display all the tags in a tag cloud? Or a flat list?
Can I display/play a youtube video in the post header?
Currently I use Poster - apart from use with foundry other reasons to swap?
See existing site here with illustration of what I am building in Poster 2 but finding rather slow to do so. Poetry Home 2 | Matrix Moments
No, it does not search the tags. It is likely though that when you write your blog posts, if you’ve tagged the post a certain way, that tag is going to exist in your blog’s body text.
Categories can be displayed this way. Tags do not have such a mechanism at this time.
No, that is not an option.
You’d probably need to make that call yourself I think as you’re the only one that can really know what you need and want. I’d encourage you to watch the videos on the site to get an idea of how Alloy works and what can be done.
Also, as you’re not using Foundry for your site you’d also need to consider that as well, as Alloy is built to work within Foundry.