Hi Michal,
You don’t need the top soil (unless you want really high beds) as it would just ‘dilute’ your compost.
Horse manure and/or compost are both fine as long as they’re well rotted, otherwise you’re just encouraging slugs. You probably need to give your horse manure a test for a nasty chemical called aminopyralid (which is becoming more prevalent again) before you use it. It’s sprayed on fields to reduce ragwort etc poisonous to horses, but the residues can end up in manure and cause distortion in susceptible veg. You can use the search facility on this page to look the test up, or maybe someone will send you a link.
You can sow your beans direct in the compost if you wish, no need to wait, but if you have a mouse problem you may be better off sowing them under cover and then transplanting. As a thought you could use some beans to test for aminopyralid at the same time and if they’re ok transplant those too.
I’ve not tried seaweed so I’ll leave that to others, but I imagine you would add it to your compost heap to rot down otherwise you’re at risk of slugs again as a mulch.
I wish you the very best with your new veg patch.
Jan
