'You know how we have ...' vs 'You know we have ...' and present verb for past event

Question

A: Get this. You know how we have those clients visiting at work next week?
B: Uh-huh.
A: Well, my boss and I were supposed to take them out to dinner on Wednesday night. But this morning, she walks into my office and tells me she can’t make it after all.

My questions:

1. Can I say without 'how' like 'you know we have those clients visiting at work next week?
   
2. If the meaning is the same without 'how', could I get more similar examples?
   
3. If it's the same, Why is the speaker putting 'how'?
   
4. 'She walks...' 'tells' are the present tense, the situation is in the past, but the speaker uses present tense. ... why? What is the effect of the present tense in the past?

Answer 1

You know I'm going to the park tomorrow?

This is really "Do you know [that] I'm going to the park tomorrow?" with the initial do being subject to "conversational elision" which can happen when speakers are familiar with each other.

You know how I'm going to the park tomorrow?

"You know how X" is basically shorthand for "Recall X (X is something I expect you to have heard before or know about), because I'm about to tell you something interesting pertaining to X that will change X."

A: You know how John always comes in late?

B: Yeah ... did something happen?

A: Yep. Well today, the boss was waiting for him, and took him in the office.

B: Uh-oh. I wonder if he is getting fired.

So these two express very different things. One is asking a question and the other is preparing the listener for further information.

Regarding 4:

Well, my boss and I were supposed to take them out to dinner on Wednesday night.

This happened last night. The past tense is obviously needed here.

But this morning, she walks into my office and tells me she can’t make it after all.

Simple present tense is often used to narrate or describe actions that are happening. It has a "disconnecting" effect - as though someone external to the activity is observing that activity. This applies even if used in the first person.

Present progressive is normally used if you don't want this "disconnecting" effect.

I'm walking to the park

This is the typical way to express that you are walking in the present.

I walk to the park

Hard to explain - but it sounds like there's a separate entity from yourself that is saying this. Even though the verb is in the first person. As though you are watching yourself walk to the park and stating that fact in observation. This concept fits perfectly if you are recounting events that just happened.

Simple present in the third-person sounds a lot less weird and is much more usual.

Answer 2

1. I would almost always say "You know how we have those clients visiting at work next week?" OR "You know those clients who are visiting next week?" I suppose you could say "You know we have those clients visiting at work next week?" but it sounds a little strange and much more colloquial. "How" is sort of a placeholder for "the fact that" as in: "You know the fact that we have those clients visiting at work next week?"

...

4. This is the historical present. Honestly, I've mostly heard it used for emphasis, usually in the context of gossip, as in "You'll never believe what Sally said earlier. This morning I was taking my walk and she comes out of her house and says..."