Questions on hive entrance

[TheFuzz]

1) Is it ever a good idea to have multiple hive entrances, not just one right at the bottom? I ask because I notice that, whenever there is a crack or hole in a hive where bees can fly out from, they seem to often prefer using that over go through right at the bottom.

2) Two of my hives have a lot of bees at the front, as show here:

https://imgur.com/a/f7aSxIE

Is this indicative of anything? Does it maybe indicate that they're looking to swarm? If I had a second entrance at the top maybe, would this possibly help with some sort of traffic congestion problem that might be happening here?

3) I built these hives myself and guessed the size needed for the hive entrance, as shown here:

https://imgur.com/a/mn0NXYh

Are these entrances possibly too small? I'm wondering if the size of these entrances could be leading to traffic congestion, or ventilation problems. I notice people talk about using entrance reducers in the winter, but I'm not sure if that's something that should be done where I live, in South Australia, which doesn't have cold winters, but gets very hot and it's almost always very dry and non-humid.

To expand on the ventilation, here's a picture of a lid I've got:

https://imgur.com/a/CA8jPFO

There's four of these holes on a lid, with a mesh barrier inside. Are these ventilation holes large enough? Some of my hives do sometimes have some moisture building up inside for whatever reason.

[Bakersdozen]

There are times when multiple hive entrances are handy for the bees.  An upper entrance will help with summer ventilation.  In winter, when the bees cluster, humidity can build up in the hive.  Condensation can collect inside the lid and drip cold water down on your bees and kill them.  So extra ventilation is important then too.  Most entrances are between 1/4 inch to 3/4 inch and run with width of the hive body.  In centimeters that is .635 to 1.905. The bees will also need this size of entrance to help reduce the moisture in honey stores.  I have seen bees reduce their entrances down with propolis.
When honey supers are on, adding an extra entrance at the top will speed the storing process for the bees. They don't have to travel from the front entrance all the way up to the honey super. Think shortcut.
You mentioned that you built your own equipment.  Bee space is very important inside the hive.  If it is not correct, the bees will make it so.  This isn't always the most advantageous for the beekeeper.

[TheFuzz]

Yikes, my entrances are significantly smaller than that. They're about 0.1 of an inch tall, and they don't run the whole length across as you can see, there's just two front entrances, some are 2 inches wide, others are 2.2 inches wide.

I've been beekeeping for years now and all my hives are like so. Some of my hives do have an issue with condensation; that is, when I open up the hive, there's a small amount of water built up on the lid, and hive mat. So it seems like my small entrances could be contributing to this? What other issues could my small entrances have?

I attached my bottom boards to my boxs. Do you think it'd be worth it to increase the size of my entrances on all my hives? If so, how big should I make them? I can make bigger entrances on my bottom boxs that don't have any bees occupying them, then I can use these to replace my boxs that are currently being used as a brood chamber, and then I can make a bigger hole on them as well.

If I cut out a bigger hole for the entrance, should I apply linseed oil or paint to where the pine is freshly cut and exposed?

[Bakersdozen]

Most of us here, in the U.S., have Langstroth hives.  Our bottom boards are separate from the hive bodies.  This makes it easier to clean the bottom boards off.  Bits of wax and dead bees will fall  and build up on the bottom.  Most of the United States has a problem with small hive beetles.  Small hive beetles can lay eggs in this debris.  When monitoring and treating for varroa mites, it's advantageous to be able to count mites that drop.  Many beekeepers use screened bottom boards as part of an Integrated Pest Management program to control varroa.
Condensation on the underside of the lid is a sure sign that you don't have enough ventilation.
The small entrances make it easy for your guard bees to control the entrance, but that is the only advantage to those small entrances that I know of.  Here in the U.S. we have removeable entrance reducers to control and help  with the traffic.  They can be made from various materials.  Hive kits usually come with a wooden entrance reducer, but mice can chew those.  But you can find metal entrance reducers.  I have used a small brick paver in a pinch.  Here is a picture of wooden entrance reducers.  You can see that in one position you can make the entrance small.  Rotate it and it's very small.

[TheFuzz]

I followed blueprints for a Langstroth hives but I did deviate on the bottom board. I actually have a single hive with a detachable bottom board, the first beehive that I bought. I've found that hive to be stressful to move, I've had the bottom board shift and the bees all come out and it was a nightmare. It has had some advantages though at times, like if I want to add a box to the bottom to act as fresh space for a brood chamber. Small hive beetles are present where I am, but they don't seem to be thriving or doing well. Don't have varroa mites, either, fortunately.

Good to know I need more ventilation, thanks. Should I just add extra ventilation holes in my lids?

Is mice mostly an issue in winter for you? Wouldn't the bees fight off a mice? Shocks me that such is an issue, it's difficult for me to image a mice getting into my hives.

Thanks for the pictures and information.

[Bakersdozen]

Mice can move in when the bees are clustered.  Where I live, the bees don't stay clustered for extended periods. 
I can't tell you about ventilation holes in your lids.  Are you using migratory or telescoping lids?  You could put notches in your inner covers. 
Many beekeepers use ratchet straps to move their hives. I use two so the hive is stabilized from both directions.  There are other means as well, I just can't think of the proper names this early in the morning.  But basically you take a small thin piece of wood, like plywood, and nail to the bottom board and brood box.  Do this to at least two sides.  That should stabilize the bottom board and brood box.  There are also 2 inch staples you could use as well.