Sorry Grill, I am going to rain on your parade mate
Just came here to boast. I beat the game last night with 2 relics on. I had another medic and 2 weapons specialist both playing the map for the first time. This was my class.
Upgraded Medic [Revive energy Raduis for 5 sec when you double tap up on d-pad, that has a small refill bar to show when you can use next, typically after 3 minutes, so use it wisely.]
High quality Armor Piercing ammo
Ammo: Armor Piercing.
Pistol: Full Auto
Team boosters [if the rest of team has armor]
Riot Shield [Put 4 skill points - 20 defenses]
Vulture. [Fully upgraded]
Relics: Take more damage & Deal less damage
Skill points priority: Since I do less damage with my guns I put my Skill points on vulture right away. This is great because when you shoot someone and during the reload the vulture finishes them off. I had double the amount of kills the weapons specialist has. About 500.
Next I put my points on Riot shield simply because even with vulture on you are prone to damage immediately, just remember to finish off breeders and sprouts as soon as possible as breeders can smoke you out with their gas.
Next I add 4 of my points to Medic, so I can run fast and revive allies with less risk and ignore gas clouds from breeders/scorpions.
Finally any skill points left I put them on team boosters
Guns: I prefer AR's and smg's to LMG's unless you are weapons specialist. My favorite gun is Honey badger and MTAR Big clip and takes 3-4 sec to reload compared to 8 seconds from LSAT. Also, Honey badger and MTAR is fun to use. Especially if you run with those in multi player games.
Crafting: I normally make sure no one touches the parts until we lay our hands on venom schematics. Then it is free for all. Once we build all our venom guns, I go for sticky flares most of the time. I craft a set of flares, then get another schematics and find parts again. Just don't craft it yet until you use the first 2. This will most likely ensure your ticket to Mc-kraken.
Favorite Venom guns: I got a chance to use electric last night for first time and I think it is my new favorite next to Fire. Only down side if if you shoot too close you may take some damage. Call out when you see venom eggs and let everyone know that you are going to spray some to go down to 2 shots before you refill your gun to 6.
Relic preference: I think for this map, you cannot go with pistol relic. Even though I have done it with pistols only relic It is very difficult to conserve ammo. Instead go for take more damage and do less damage first. Relaxing End has completed this with all 5 relics in co-op mode so there is hope for those pursuing such a daunting task.
Finally it all comes down to Mc-Kraken. One word ARMOR. Throw lots and lots of armor. Grill has made excellent points already. I will just add finishing touch. If you have randoms that insist on staying in the circle, you are a bit out of luck unless you are the guy with ARMOR. Unfortunately I was carrying team boosters. The reason I say this because it is very crucial to stay in the corners when battling Mc-kracken. Not only does it it keeps your backs covered from hundreds of aliens it will allow you to shoot the aliens easily with one guy focusing on breeders and Mc-kracken at the same time. Remember not to waste your money if you are running low, use it only if you must. And wait until you absolutely need the armor before you grab a new one. Also, you only get 2-3 seconds after the warning from your squad mate about Mc-kracken's weak status. At this time you better stay in the safe area. I died twice yesterday trying to grab venon ammo. It was just bad timing.
A very helpful tip (Share your money): If you need ammo and a friend is doing ammo, instead of asking ammo it is better to share some money so he will give out ammo when you are really in need and you are short on funds. Press and hold Left trigger (Ads) and A (Jump) for at least 4 seconds to share money. Remember to say " This is for the ammo/Armor guy". And curse the ones that throw armor that is not upgraded. It is just not worth wasting the money even if it is not yours. Team work is what wins games.
Oh btw I have purchased this Seeker protection plan from armory. It helps a ton because seekers are very annoying and sneaky for this map.
Sorry for a long post but I really think it helps someone trying to beat with relics. All the best and share your stories. It will help encourage others to play and beat the map which is ridiculously fun for first person shooters.