Yes you are correct
A 10-foot-radius immobile dome of force springs into existence around
and above you and remains stationary for the duration. The spell ends
if you leave its area.
This paragraph solely focuses on what happens when the spell is cast including when it ends. The dome ends after 8 hours or when you leave it.
Nine creatures of Medium size or smaller can fit inside the dome with
you. The spell fails if its area includes a larger creature or more
than nine creatures. Creatures and objects within the dome when you
cast this spell can move through it freely....
This paragraph (and the omitted part) references what happens to the things and creatures inside the dome.
The use of the word "can" implies choice.
Any other time the word "can" appears in a ruling, it means that the thing is possible if you want.
Take the Combat rules for example:
On your turn, you can move a distance up to your speed and take one action.
You can forgo moving, taking an action, or doing anything at all on your turn.
You can take only one bonus action on your turn
Your turn can include a variety of flourishes that require neither your action nor your move.
You can communicate however you are able, through brief utterances and gestures, as you take your turn.
You can also interact with one object or feature of the environment for free, during either your move or your action. For example, you could open a door during your move as you stride toward a foe, or you could draw your weapon as part of the same action you use to attack.
If you want to interact with a second object, you need to use your action. Some magic items and other special objects always require an action to use, as stated in their descriptions.
All these things are optional. You do not have to move up to your speed, but you can if you want. You do not have to forgo moving or taking an action, but you can if you want.
Note that it does not say "If you want to interact with a second object, you can use your action, it says you need to use your action. This is because there is no choice, you must use your action.
Leomund was a smart guy
Given Leomund's history, I don't think he would leave such a glaring oversight in his spell. It would make the spell largely redundant, as you could simply remove the earth under the hut and the occupants would walk through.
As shown in this article by Nerdarchy, Leomund was a smart guy. I don't really believe he would design a spell like this with such a large flaw in its design.
I would say the biggest reason Leomund is one of the famous wizards of distinction is because of his inventiveness. From the number of new spells he created to their utility in boosting the survivability of an adventure, Leomund had an answer.
I refuse to believe that such a clever and inventive Archmage would create a spell with such a simple flaw. I think he can design a working floor.
Conclusion
I would personally rule that the player can choose whether or not to pass through it, since the wording of the spell is in line with that and that would be best for my group. I also think it makes more logical sense if they are given the choice to pass through or not, since if you just passed through the bottom of the Hut, the floor is purposeless. There's no point to it if you have to phase through it and sit on the ground anyways.
TL;DR: Yes, they can pass through the floor if they want or they can
choose to not pass through the floor and collide with it if they
want.
However, I would also say that each DM should do whatever they think is the most fun for their group.
Best Answer
Yes. You can move a familiar outside LTH
The duration of the find familiar spell is instantaneous
meaning that after the initial casting there is no active spell to dispel.
Yes. You can cast spells through the familiar
Yes, while you are inside the LTH, you can cast spells through your familiar as the range of the spells is touch. The spell is cast by the caster with an origin at the familiar and has a range of touch. Never does a spell pass through the barrier. The spell does not pass through the barrier effect and is therefore not blocked.
These have been talked about in this question about what part of a familiar is magical
LTH wont end
Having the familiar inside during the casting means that it won't exceed the creature limit and the familiar moving outside the hut won't remove the hut.
You are still inside the Hut.
D&D counts bodies, not minds. You are still there unless you move out. Your familiar isn't you. Therefore, the hut will remain intact. (The DM may rule that your mind must be inside the dome in order to maintain the hut, but by RAW it doesn't.)