Taxi from Haneda Airport to Taitō

Good evening,

I've got a couple of questions about traveling by taxi in Japan and hope you can help me out.

Some background information:
My friends and I will arrive at Haneda Airport (International Terminal) at 10:45 p.m. on a Sunday. We want to take a taxi to our accomodation "Khaosan Tokyo Laboratory" (in Taitō, Tokyo, near Asakusa station).

Now we have the following questions:
Is it easy to get a taxi from Haneda Airport to Tokyo City (Taitō) at a late hour or do we need to reserve a taxi?
Does it matter how many persons will use the taxi (regarding the costs)? Or in other words: Does the number of passengers influence the fixed fare?
Are there any hidden costs that we have to consider (we are already aware of the highway toll fees)?

Thank you very much.
Julia

Is it easy to get a taxi from Haneda Airport to Tokyo City (Taitō) at a late hour or do we need to reserve a taxi?
Regular trains still operating, use Google Maps or HyperDia web.
https://goo.gl/maps/EV7uRTA21A52
Taxi, no need reserve, but reserved "fixed fare" one may better.

Does it matter how many persons will use the taxi (regarding the costs)? Or in other words: Does the number of passengers influence the fixed fare?
Taxi charges do not affect the number of passengers, but taxis have "Small, Midium, Large" classes,
there are only "M" and "L" in Haneda.(even in mid Tokyo)
The standard taxi is a sedan type, 4 passengers mainly but not only one type.
Now newest ones are increasing for Tokyo Olympic 2020.
https://toyota.jp/jpntaxi/

Are there any hidden costs that we have to consider (we are already aware of the highway toll fees)?
Expressways tolls are linked to a taxi meter, no worry, taxi won't be stopping toll gates.
http://www.go-etc.jp/english/benefits/index.html
If no big traffic accident or constructions, seems around 10000Y, 30 min,
including Expressways toll "780Y" and mid night rate 20% up, also sales tax 8%.
https://goo.gl/maps/87tcTn2p5FU2
(This is not including taxi fare, just a route.)
No need "tipping" for a driver, also no need to touch the taxi rear left door when open and close.
https://youtu.be/ynNdAHuTS18
https://youtu.be/EN_Ju5l7T5c
https://youtu.be/T4WN7KcuzM0

Thanks a lot for your effort and advice, Gah8!

Best regards
Julia