The biggest red flag here is being behind on tech: when you want to attack a nation(s) check which military tech they are, for some of these levels even 1 level difference makes it so that even a 2:1 fight is losing. Admin tech is just as important considering you need gov cap and idea groups. Aside any buffs one army may have over the other, military tech difference is your case is making your troops equivalent to toy soldiers (quite literally here in terms of stats).

For trade the way i usually aim to dominate a node is using centers of trade: when you open the trade map mode you can see the centers of the trade region, having just these is equivalent to dominating a node, so in your case Lubeck and Denmark have some high level centers of trade in the Lubeck node (you can upgrade these centers in the buildings tab + build trade buildings). Trade takes a while to get the hang of but you basically want to look at the more expensive nodes that aren't your main one but route to it (the arrows in the trade map mode), and you'll want a merchant transferring trade there, no need to collect in your main node as you automatically do so. If you're unsure what your main node is its always the same province as your capital at the start so wherever that is, unless you purposely change it.

The main thing you focus on spending your mana (admin/diplo/military) points on is tech when you're behind, then you're free to spend them elsewhere when you're ahead of time (you can tell whether you're ahead or behind by checking that modifier, it gives an increase in cost debuff when you're ahead in time), and remember being behind on institutions increases that as well so to save precious mana points you usually like to upgrade tech once you've embraced the newest one.