If you're going to attack the train room. Please don't huddle around the window that peeks into the room, the one that's above the bakery. Let Blackbeard work it, if he want's to, but be careful with c4 raining down from the window above, and a jumper from the window next to the stairs that lead into the train room. Go for the hatch above the train room, just scan it out nicely. Check for trap, cameras, and hiders. Once the hatch is open, don't all group around it, use your team and cover your flanks.
If you're attacking the kitchen, you need to breach the front of bakery. Use the windows to your advantage, have a man cover the stairs, and another man blow a hole in the wall between bakery and the little mini kitchen prep area, this will cover you on both flanks. Don't forget above the area above, enemies will try to come out through the train room and take you out, listen for breaks in windows. Don't enter one by one, spread your team out and break in from different entry points. Push the fridge, push the bakery side, and push the main entrance to the kitchen. Don't forget about your flashbangs, and please don't shoot the hostage. If you think Bandit is up to no good, and he's trying to bandit trick you, blow that side window in the kitchen prep area, this gives you a nice viewpoint into the wall that he's working. Just watch your right side, because you will be vulnerable from that door that leads into the rear of the fridge.
Defenders, if you're in the train room, don't crowd up, it's a freaking death trap. Utilize those roamers, use those traps, put down that barb wire. Cover the floor above to the best of your abilities, this is when sneaky Valk cams come in handy. Wait for the perfect moment to strike the hatch breacher, don't just rush in the room, and for god's sake, don't mark on the camera, use your mic's people! The objective of the roamers is to support the two defenders in the objective, don't just go for kills, help these guys out, because if it's down to just the two of them, it's going to be tough, they have a ton of areas to cover with little cover for themselves. If you're in objective, call out where you are taking fire, if the hatch is hot, let one of your roamers know, they can hopefully sneak over to it and take the attackers out. Just be careful, more than likely a good team will have a guy watching the stairs that lead up to the hatch, so be prepared for a firefight.
If you're going to defend the kitchen, you cannot allow thermite to breach the main wall that faces the bakery, the one that needs three reinforcements to cover. Utilize your cover wisely, cover up the bakery side, and use the remainder for the fridge, this usually just leaves on open wall in the fridge. Once again, utilize those roamers, cover the rear of the fridge, use Jager to cover long lanes of fire, you can find some nice spots that look into the bakery, and don't rush into the bakery, the attackers have the advantage in the bakery, concentrate on preventing that thermite and cover Bandit. This is why I like to castle that wall that leads into the kitchen from that mini prep area. If you have a big pair of cohones, try and pop out from the roof area above the bakery, use the window that leads out from the train room. You can usually take out some of the attackers posted on the windows this way, or at least create enough of a distraction to peek into the bakery with a good shooter.
Overall I find Kafe to be a balanced map, it's a little difficult for defenders to hold the objectives, and you need to utilize roamers. Just don't leave the objective empty. Use your drones wisely, try to save some from the prep phase, Kafe is big, so don't loose too much time scouting. Use communication and please be careful with spawn peekers, wait just a few seconds before moving, trust me.