How do you communicate with your team members? For me it has always been: turn around and ask. Or if they look busy, wait until they get a coffee before interrupting.
I never worked in my own office (I'm 39), so I'm really curious what you prefer: phone, email, knocking on someones door?
Also, how do you stay in the loop about what's going on?
Not OP, but I am lucky enough to have my own office with a door. Everyone in my group just leaves their door open if they are available to be interrupted. I communicate entirely by email and in person. If it's a quick thing that I only need a verbal response to, I'll usually walk over and see if the person is in their office (w/ door open) first. If not, or if I need something more substantial, I'll email.
On the flip side, most of the day my door is open, and I don't mind occasionally being interrupted to help someone else with whatever they need. If I have a conference call or I just want to really focus on something, I close my door and it's unlikely anyone will knock or otherwise disturb me unless the building is on fire.
I have an office with a door and I love it (but no windows to the outside, unfortunately). If I'm on a call or just want to be able to work uninterrupted for a while, I'll close it, otherwise I'll leave it ajar so colleagues can stop by if they have a question or want a quick chat. I work in product R&D; the building also has a cube farm area for IT and HR and business folks, so I'm really happy I'm not there.
My team is distributed around the world so my team collaboration is all virtual, although my management and some of my [internal] customers are located in the same building as me so they can stop by my office or vice versa if we have things to work on together.
It's a wonderful, comfortable way to work. Your ability to concentrate is respected. It's overall a much quieter environment conducive to solving problems. You'll loop in yourself during lunch, at meetings, getting coffee, passing by other offices/being passed by, etc.
Not OP, but Slack/IRC/IM of some kind is the answer to most of your questions. I've bounced around between shared office, private office, cubicle, private bullpen, and open office my whole career, and by far the least productive I ever was was in the open office. In all other situations, my team communicated mostly over instant messaging, or if it was really important, by wandering down to their office and knocking.
Since most team communication happens over IM, it's easy for anyone to read back on what they missed. Most teams also do daily stand-ups or other meetings, to catch the larger group up on anything important.
FWIW, all the places I've worked that had offices in whole or in part had a culture in which everyone left their door open unless they didn't want to be disturbed for some reason. Collaborating was never an issue. If everyone always kept their doors shut, I think I would have found that hindered communication, esp. pre-IM.
I'm 37.