will the game consist of constant combat, or will there be periods of relaxed, "don't worry about the base" mining and exploration? I mean, war is fun, but with so much planned to see and do, I'd like to be able to take it easy and bumble around a bit.

Well, about anything is moddable, so if the game isn't slow-paced enough for you, then you can mod it the way you like it.

Yeah, when/if the campaign editor comes out, you'll be able to customise the levels alot more.

it IS out >.> or... nvm you probobly mean the new one

It depends how well you set up your base and how well you have placed the defences for your brain. If your fortress of doom is covered with snipers/turrets/soldiers in all directions, you can go and do something else while it stands. While mining though, you can quickly check if the base is still standing and take measures if needed.

This applies to the current build of this game. Maybe when we get Lua, areas, scripts and campaigns and a metagame, then it might be different.
I dont know about that so time will tell.

Yes, I mean the new one announced in the latest devlog. You'll most probably be able to set intervals between waves and idividually configure waves of enemies and automatic reinforcement.

would it be possible to make dropships spawn nothing for a few round giving you some peace time?

Yes, probably. I think that by adding in dropships with no cargo with more powerful engines to your activities.ini in between your normal ones, you could have the occasional lull. However, your activities would become engorged, meaning more room for a mistake.

Not if you test it and then just use copy & paste.