Missions & Complexes

Noticed that just a minute ago E.E. after looking at the "new" tracking computers more closely. They have a falloff bonus now that's boosted along with the optimal range by the script - nifty. Forgive my module knowledge for being a few years out of date.

X-Large Shield Booster and Heavy Cap Booster are pretty much a must - Unless you have a Gist X-Large Shield Booster (and those are bloody expensive)
You don't need the Cap Booster that often, most times you can just burst tank without needing the extra cap, but they're extremly useful when you trigger/aggro too much or fly the harder missions.

How to choose between Tracking Enhancers and Dmg Mods is about what your ship (and the weapons) lack and how many low slots you have for this.
On a Maelstrom you lack range with Autocannons, as they are close range weapons and you generally lack damage, as you can't have ever enough of it.
So with my Artillery Build I use 4 Gyros as I don't need extra range and 1 TE - Why not 5 Gyros you might ask? That's because of stacking penalties. The more Dmg Mods you have on your ship, the less any extra dmg mod will add:

Modules Effect of nth module
1 100%
2 87%
3 57%
4 28%
5 10.5%
6 3%

As you see a fifth Gyro would only add 10.5% of its initial boni, a TE is much more useful.

With my AC Mael I chose 2 TEs to bolster my range - More range is more applied dps for close range weapons (less for longe range as the basis range puts most enemies into falloff if not optimal - The effects of a TE are much less useful there)
Now I only have 3 Gyros, but as the 4th only adds 28% of its bonus, it's still a good trade.

For BC <-> Gyro take a good look at the modules - One applies to Missile Launchers (the Mael doesn't have any) and the Gyros apply to Projectile Weapons.

The Rigs are in there as they give the most cap advantage out of the slot. Capacitor Control Circuits (CCC) add less flat cap (due to using a Cap Booster instead of Cap Rechargers), while the Core Defense Capacitor Saveguards save quite a bit cap (due to the high cap cost of the Shield Booster).
Shield Extender/Purger are for ships that tank with a passive tank. The Maelstrom depends on Shield Booster and those are independent from both the shield recharge rate and the maximum shield hp and thus doesn't use those rigs.

There are no definite rules for modules and rigs - None that I could come up with now, besides some more obvious ones - Not more than 4 Dmg modules, use the right Dmg modules (No Ballistic Controls for non-Missile Weapons)

You should download EFT, import your skills and play with fits - You can see the effect different modules have on each ship very easily there.

Your missile skills are incredibad. Like really really. If you want to go missiles (and have a proper opinion of them) you are looking at about a mill SP in missiles and support skills.

That said For low SP oyu want an ARTY mael, and you need to know HOW to fly it and you'll do fine in missions. They are rather attention intesive as you need to switch stuff out every now and then but you can do one easily without cap boosters. Just learn how to burst tank.

Important note, Mission battleships are pretty much all active tanked and its normally a very bad idea mixing active and passive tanking.

I can tank lv4s with just 2 hardeners, shield booster, shield amp and 3 CCC rigs. Mael is pretty easy to overtank at first. I use two tracking comp IIs to boost tracking on the arty and group the arty into 4 groups of 2 to help minimize lost dps. also you NEED T2 scout drones. Sentries are nice since they do damage soon as you drop them while heavies have rather long flight times to ships.

Ravens are easy, low attention and boring but without any tank bonus they need cap boosters and at LEAST 1 mill in missile skills. Have a look at the missile support skills, you are missing out on tons of dps.

https://forums.eveonline.com/default.aspx?g=posts&m=872354#post872354

Read the whole thing, its pretty good (my post best tho :P )

Seriously, with the missile skills you have you should not even be allowed into ANY missile ship.