I would strongly advise against using beams for anything other than an anti shield ion beam, and even that is seriously iffy for a large, slow moving titan, as it could take you a while to get in range, by which time it may be moot. If you do make such an ion beam, make it beam/beam/ion in equal measure, you want the range. Because you are slow, you will not be able to pick your range very often, except maybe versus stations. You should plan accordingly.
Stations will always be armed with maximum range missiles (missile/beam). You may think this is a good reason to go with closer ranged weaponry, but your slowness will mean it will take time to get in range, all of which time you will be under fire. I would recommend going heavy either all in with maximum range missiles yourself, or with a mix of such missiles along with cannon/beam/punch turrets, leaning more towards the missiles. Make sure you've got really good point defense so you can win a missile war. Make sure you've got a good quantity of tiny decoy missiles firing along with your heavy offensive ones, to bait your enemy's point defense.
Put maximum power on your ship, make sure you've got insane quantities of power capacitor storage (and that your surplus power is sufficient to fill it), and calculate how many modules you'll need in missiles to use up that stored power every 45 seconds. Factor in of course the power requirements and storage for your cannon/beam turrets as well.
The main reason most people's ships can't fight their way out of a wet paper bag is because they don't have enough power. Don't make that mistake. Figure out how to have insane quantities of power and then use all of it. To give you an idea, my 350K mass battleminer generates 80 million power per second. That's not capacitor storage, that's what it generates. Don't do like most people and figure that a couple of auxiliary power sections will do the trick. Your combat power is 100% dependant on how much power you can generate.
A large ship should be able to easily accommodate turrets with 4000 weapon modules or more, especially if you build ball turrets. Though if you are wanting to keep the turret numbers down, you might want to increase the weapon module count well beyond that.
Offensive missiles (not the decoys) should be built with at least 150 modules of missile/beam/explosive in equal measure. I usually make them quite a bit bigger than that (450 total), to make sure they can handle multiple layers of armor. Remember that if you are putting these in turrets, there is absolutely no reason you can't have multiple missiles firing from the same turret. Also remember to have decoy missiles mixed in with them.
Cannon/beam/punch should also be used in equal measure for the guns. Those do not need to be particularly large to break advanced armor, as little as 100 modules will do. Your turrets should break up the volume you have available for such cannon weapon modules into several smaller weapons lest you build a weapon that will punch only a single tiny hole, right through your enemy ship. That may sound great, and it is if you get lucky and hole an aux reactor, but a whole lot of your potential damage in that instance would be wasted into space, on the other side of your enemy. Best to punch multiple holes.