1. Night and day. Go2 vs Go2 is all about bringing a win-condition. You will not win by just trying to survive - you need someone like Rotos or Mortu, that can provide a slowly-building advantage. Otherwise, you end up locked in an infinite fight. Go2 vs speed-nuke is all about surviving the burst. You don't really need any win-condition at all. Typically, if you survive, you win. Now - things certainly can get more complicated, especially when you're up against a more hybrid-oriented setup such as Arbiter + Siphi + Ursaga + Candy, where they're still trying to win the speed race, but even if they lose it, they'll probably still survive. More on this in ...
2. This point. My suggestion - don't waste your time trying to do both. Build your Go2 to either face speed nuke, or to face Go2. If the former, you need tools to mitigate the incoming damage. If you're lucky enough to have Duchess, Stoneskin Duchess is very, very strong. If you aren't, look for people like Boragar, with powerful passives, to help you survive. Bolster + Shield + Brogni is also a very strong survival tool. If you're going for Go2 vs Go2, make sure you have a win-condition. Like I mentioned earlier, Rotos and Mortu are very strong here. There are other, more niche win-cons, typically people who just do a really, really large amount of single-target damage, combined with sets like Destroy. But I would probably just avoid wasting resources on this type of team unless you have Rotos or Mortu.
3. See point 2. Typically, you'll want Mithrala, and if you're going vs Go2, you'll want at least one reviver, if not two. Vs speed nuke you'll want Bolster + Shield, so two people with high max HP. Don't waste time with resist - just get Mithrala with high RES/ACC. You won't win the arms race of resist vs accuracy.
4. You'll want around 200 speed on everyone. Faster is nice, but not mandatory. Slower makes it dangerous, since they could start lapping you. You'll want Mithrala to have a combined RES+ACC above 750. Everyone else, you'll want a modicum of resist - maybe around 350. Nothing extreme. Accuracy is largely irrelevant - against Go2 you aren't landing any debuffs, and against speed nuke they have no resist anyway. HP champs want HP>70k, DEF>2500, DEF champs want HP>60K, DEF>3200.
5. Avoid any team with Mortu. You'll almost certainly lose. Avoid Trunda - she just hits too hard. Hephraak is also probably someone you should avoid, though you can roll the dice if you'd like. Candy is a bit of a dice-roll, but personally I usually fight him. Most other nukers are very much doable. Avoid teams with Kimi, since they often are much more dangerous than they look. Avoid Baron. Hard stop.
6. You probably won't be subbing a whole lot, so don't worry too much here.
7. As mentioned earlier, Brogni + Bolster + Shield. Also, Brogni + Mithrala. Really, just Brogni.

Thanks, Kram. Don't have Brogni, but I'll keep him in mind. 

I was thinking about building 2 go-second teams for Tag, that's why I'm wondering how to split them and who to fit what roles, as well as which to use against speed teams and which to use against go-2nds I have champions for 2 speed nuke teams, but Speed gear avoids me like a plague. The champs I have built for go-second are:

Lydia, Tuhanarak, Duchess, UDK, Rotos, Vogoth. I'm building Basher to substitute Krisk in my Speed team, so Krisk can go in one of the go-seconds.

Waiting for Mithrala, and I have Candraphon, Cruetraxa, Elva, Maulie and a few others unbuilt/ungeared. 

krama makes good points, one comment though- on defence an annoying 'infinite fight' team is not necessarily a bad thing. 

I would probably go with Mithrala, Duchess, UDK, and Rotos. Put UDK and Duchess in Stoneskin, and go up vs speed-nuke teams.

I think this is your best team myself.

I might put Duchess in High Resist Swift Parry though, myself. Close to 260 speed as you can get with high resist. Then tune Mithrala to go right before her, 1ish speed faster, ofc with sweet sweet accuracy resistance.

And for now, since you don't have Mithrala yet, go with Duchess, then Tuhanarak in a Bolster set, UDK in Stoneskin and SLOW, and Rotos. Tuha is playing a budget Siphi to keep Rotos cleansed here. Sure, she's no Siphi, but we go with what we've got.

Awesome. Thanks, guys. If I'm up against a reviver, should I bring Lydia along?

Another question: if I'm not likely to land debuffs on the go-second teams, what is my play? Buff my team? Rely on players who are strong without debuffs? Sustain until Rotos builds up HP?

Number 3. Enjoy the 15-minute fights :)

Sustain. Once Rotos gets going, it's OVER.

I don't mind. Manualing Arena fights is a guilty pleasure lol 

Wait'll you need to spend 30 minutes on each tag fight, and that you need to win those fights to reach your rank, and that you just lost a fight because you got five weak hits in a row at a bad time, and it's Sunday night and you want to throw your phone out the window :)

We gotta find you a faster team, Kram. lol

Although sometimes Mortu gets hit 30 times without a single Peril proc and you go 2-1 instead of 3-0 or 1-2 instead of 2-1 and BOOM, you're in Gold 2 now. "Enjoy your stay this week!" -Stupid Lazy Mortu

That's my clansmates' problems right now lol 

I'm far from Ramantu quests. Just got Arbiter not too long ago, still on Upgrade 3 Great Hall Bonuses to lvl10 quest. So figure I got time to practice. 

Enjoy UDK or Duchess with stoneskin and new defiant set... maybe if you feel your team weak, just put there a Nekreth and Mortu too beside of first two hero.

I don't have them. I see Nekhret protecting the gllass cannons a lot. I think at this point, it's a lot of testing the waters. A lot to learn about strategies and tactics, it's what I'm learning to like about go-second teams. Speed nuke team is efficient, but it's more or less the same.