Missions & Complexes

Generally speaking, how much dps you have to tank on level 4 missions? And over how much would it be overtanking?
Ignoring specific scenarios and not trying to tank all the ships at the same time (such as AFK missioning).

For starting out that's pretty fair, especially if you're armor tanking. Make sure that's on mission-specific resists though.

Shield tanking can be lower sustained and higher burst due to shorter cycle times and rep at the start of cycles.

With time and experience, your sustained number gets less and less important. You learn the missions and get more and more gank going, meaning tank only comes into play for a fraction of your time in each pocket. I have a Sleipnir build that has served me well enough in missions that only has 52 seconds of cap -- but it's never needed that much. Most non-injected Machariels clock in at about two to three minutes cap with tank running, less on MWD fits.

Burst tank of 350 which lasts for around 4/5 mins is enough.

When I ran with the nightmare I ran with a 800DPS tank and +/- 1100 DPS, the cap lasted like 1 min if I ran everything, but I rarely used a cap booster as the DPS is monstourous and rips through just about everything.

Also if you have range and speed such as an ab tengu you barely need to tank, you will take very little damage in general. I find that when missioning in a gila only one lse is required to tank the missions due to a smallish Sig and speed.

Yeah, I had to warp away and refit during a Worlds Collide. One repper wasn't enough =P
But it's all part of the learning experience, trial and error.

An AF / stealth bomber duo make for some amusing & different pve particularly given the nature of sig/speed tanking. You should even be able to get away with pvp fittings with a little luck, particularly on the AF.

First things first...

800 tanked DPS in a battleship is the same as a Tengu with 140 tanked DPS flying at 600m/s. So, if you ever go into t3 hulls, that is a new world.

However, each rat is different.

Angel does less damage, but then, takes less damage. Sansha on the other hand deals more damage and the freaking Tracking Disruption, but melts down like butter against a hot knife.

That said, keep in mind that armor tanking is a LOT different than shield tanking, mainly due to the reps cycles and the Inv. Field.

Start safe, but whatever you do, keep 3 DPS mods (Gyros, Magnectic, Heat Sinks, Ballistic) in the low mods. If you can't do that, there is something you could probably review, although some fits are tricky.

Make sure your fits can hit about 70kms with 600 DPS. Do NOT go for Arts / Tachyons / Rails just for that. Tracking is more important and helps to get rid of cruisers quickly.

For shields, sell your cat, I don't care, get yourself a Gist X-large. That will allow you to run for ever. Another option is the X-Large + cap booster, but I'm really not a fan of having to keep track of boosters.

And, if your DPS skills are low, aka, under 500, you might wanna stick with L3s for a bit longer. You'll make almost as much ISK as running L4s slowly, without all the risk. Kill them faster than they can kill you works wonders in missions.

My Raven has a C5-L and one Amp, along with one invul and 2 specific hardeners. I have the option of an afterburner or second boost amp for the final mid slot. With the AB, I can out-range most battleships and use a nearby cruiser to vampire capacitor from. The Fit gives me 2 minutes of Cap w/o AB running or stable with AB but no booster. So if I can outrun most damage (250m/s) then I'm stable, otherwise I have 2 minutes of constant booster.

My plan is to upgrade to Navy Raven and then cut out the second amp (if I find that with the AB I hardly ever run the booster) and fit a painter.

One very good thing, if the fight goes on a while, and you retreat from the pack constantly until they are all dead (I have 120km range) and you find yourself over 150km from the gate, you can warp there once all are dead. My Noctis has MWD so has no problem retracing the line of battle and warping to the gate also.