Howdy- new player here, I recently submitted a registration request but wanted to go ahead and ask a few quick questions about this wonderful game

1) I am struggling to understand how I should set my beam weapon fire controls to shoot at missiles. I read somewhere that railguns are good beam weapons to use against missiles, so I designed a class like this:
20 cm railguns 2x4 range 200,000 tracking speed about 7200 and a rate of fire 20, with a secondary armament of 10 cm railguns 4x4 with a range of 50,000 tracking speed about 7200 and a rate of fire of 5. The primary and secondary batteries have segregated fire controls based on their caliber, and the fire control has a range of 256,000, tracking speed of 12,0000.
My problem is I have no idea how to make this set up actually shoot at the enemy missiles. It works great against actual ships- I just have to target them and "open fire." But against missiles, and the enemy has shot hundreds at me so far, I can't seem to get so much as a shot off. I've tried area defense vs ranged defensive fire vs point blank defensive fire, and the system doesn't seem to fire at missiles automatically if I leave the missile fire controls inactive (but still mapped to my railguns), but if I leave my fire control "on" with no target selected, it doesn't seem to target the missiles either? And clicking "Fleet fire at will" doesn't seem to cause them to target missiles either... For reference, the main enemy missile is about 20,000 km/s, so while I don't expect wonders out of my beam weapons, I assumed I would hit something sooner or later (?)
Fortunately, I am so far ahead on engine and shield technology that my ongoing attempt to teach my nearest neighbor that Blowing Up Survey Ships Without Provocation Is Rude has been only slightly impeded by the enemy missile attacks. However, I want to make sure I learn proper beam missile defense settings for when I run into more of a peer competitor.
2) While on the topic of anti-missile defense, when I eventually try an anti-missile missile set up, what fire control settings should I use for that missile fire control? Will it automatically launch on incoming missiles if I map a missile fire control to an anti-missile missile launcher?
3) I hear Gauss cannon are a good late game missile defense technology- should they always be set to point blank defensive fire, or are there other viable strategies? And as before, should you set your fire control on or off for them to identify and target enemy missiles?
4) Finally, I saw that a size one missile seems to automatically assume it is an anti-missile missile. Is there any way to create anti-missile missiles larger than size one?
Thank you in advance for any advice- this game is a work of genius and I am grateful for the opportunity to play it.