To me, the fun part about this game is how the questions in this thread depend so much on other factors beyond ship design.
So, tonnage depends a lot on shipyard sizes, maybe even which slipways are available, and jump engine sizes. I'm in the early stages of a game building 4kt ships because I build some 4kt jump engines to get my survey ships out into the universe. But, now I'm getting jump gates build between the good systems my surveyors found, and I'm starting to be able to think about much bigger sizes. But with the proviso that those bigger ships would still only be useful in the systems with the jump gates.
Maintenance questions are the same way. You kinda have to ask yourself first where this ship is going to operate. If you are sending your ships out on long 5 year missions to go where no zwardnik has gone before, then they need more maintenance than the ships that I know from their size are designed to operate only in the systems connected by jump gates, and thus presumably always close to be able to be resupplied to top up their supply stocks and keep the parts from breaking down.
Maybe because I'm an engineer type, but to me the fun part of this game is trying to build ship designs that fit your circumstances and needs.
And like you, I'm in one of the first games I've gotten this far trying to build ships to fight against enemies I haven't seen yet. So, there's a natural uncertainty about whether what I'm building is good enough to fight against an unknown foe.
Did learn a few things from this thread. So thank you very much both to Atlantia for starting it and for everyone who joined in. I suspect my missile defense is of too short a range. I went for fast, small missiles with a range of only 200k km. Sounded like I heard some good tactical advice higher up that they like to engage incoming missiles further away than that.
I was just going through the 'big' versus 'small' missile debate on my own. I'd designed some size 12 missile and MIRV'ing drones for my planetary defenses. And then went ahead and designed a shipboard size 12 launcher just to give myself the option of moving these missiles out away from my planets. So, I was then debating between new ship designs that either expanded out then number of tubes firing my current size 4 missiles, or instead having a few tubes that could fire the big missiles out at an enemy. Last night, right before reading this thread, I'd already descided to go with the plan of smaller but more missiles. Hopefully that'll overwhelm any PD defenses with numbers. Although, if I get a shipyard free'd up, I might still put out at least a few of the size 12 big tube ships just so I can be more flexible with that missile stockpile.
Don't forget to think in terms of Task Groups instead of individual ships. The key seems to be in what combat power a group brings to a battle. You've already started that in terms of escorts and strikers and sensor ships. But you can also have a supply ship around restocking the fleet on those MSPs. Or tankers. Or ordinance ships. Sounds like that can be important to remember, especially if working under a size limit or if trying to keep your combat ships as small and as fast as possible. I just try to make myself think of the task group that will eventually be fighting instead of looking just at the class design on the screen in front of me.
Don't forget beam ships either. Like you, I think I tend to undersize my magazines. Especially since I was working, and still am for any offensive fleets, with a 4k jump engine limit (a 7. 5kt mil jump engine is being researched). But all this talk about magazine sizes also starts to reveal the advantages of a ship that doesn't need ammo. So, I've been trying to mix in some Beam ships into my construction plans. I've also got a couple of planets the surveyors have found nearby that are planetary nebula where missiles won't work anyways.
Names like Frigate and Cruiser are just for your own use. Make them whatever you like. You can type new ones on the list at the bottom if you want. So far, figuring I was doing little ships that fit through my little jump holes, I've been calling my Frigates, with the newer 7k designs being called Destroyers. But, that's just my own preferences and you can call them what you want. You can make Dreadnaughts be little patrol craft and save the ultra scary name of "Destroyer" for your future Death Star if you want.