I just setup a two access points using 2xEthernet ports of 1xRB433AH with 2xRB951UI-2HnD-IN. Is it possible to add some more access points?

2 x AP via ETH ports with 951 configured as AP ... already done
+
3 x WiFi interfaces as add-on cards and antennas

Result: 5

Take dual band interfaces, use virtual APs, so you can have 8+ and counting, and the question starts to sound strange...

Take dual band interfaces, use virtual APs, so you can have 8+ and counting, and the question starts to sound strange...

No. It's your answer that sounds strange to me now. Could you explain it in detail please?

2 x AP via ETH ports with 951 configured as AP ... already done
+
3 x WiFi interfaces as add-on cards and antennas

Result: 5

You mean I need three more wlan cards to interface with 433 and 2 of 951?

It depends on what you're trying to do. If you add three wlan cards to RB433AH, you'll have three new wireless interfaces. And then you can use them as three separate APs. You can also add virtual APs to each physical interface, but those will share frequency and bandwidth of base interface.
You can also connect switch(es) with enough ports and connect as many other RBs as you want.

It depends on what you're trying to do. If you add three wlan cards to RB433AH, you'll have three new wireless interfaces. And then you can use them as three separate APs. You can also add virtual APs to each physical interface, but those will share frequency and bandwidth of base interface.
You can also connect switch(es) with enough ports and connect as many other RBs as you want.

I made 433 CAPsMAN and 951s as CAP. Suppose I want to use the available wireless interfaces (1 of 433 and 2 of 951) for new access points, then will 433 manage those 2 APs which are setup using 951 wireless interface?

2 x AP via ETH ports with 951 configured as AP ... already done
+
3 x WiFi interfaces as add-on cards and antennas

Result: 5

You mean I need three more wlan cards to interface with 433 and 2 of 951?

No.
433AH has no WiFi interfaces so you can add max 3 cards to make max 3 real AP.
As it was written you can make virtual AP interfaces to make virtual networks.

1 x eth is needed to feed data to/from 433 so you have 2 eth ports left to append APs.
As it was written you can connect to it as many AP as you wish but if I count one port per one AP then the total result is 5.

Virtually you can have as many AP as you wish ....
Connect all your RBs to this 433AH, install CAPS on all of them and voila ...
you have all external RB's WiFi interfaces "connected" = managable from this 433AH.

2 x AP via ETH ports with 951 configured as AP ... already done
+
3 x WiFi interfaces as add-on cards and antennas

Result: 5

You mean I need three more wlan cards to interface with 433 and 2 of 951?

No.
433AH has no WiFi interfaces so you can add max 3 cards to make max 3 real AP.
As it was written you can make virtual AP interfaces to make virtual networks.

1 x eth is needed to feed data to/from 433 so you have 2 eth ports left to append APs.
As it was written you can connect to it as many AP as you wish but if I count one port per one AP then the total result is 5.

Virtually you can have as many AP as you wish ....
Connect all your RBs to this 433AH, install CAPS on all of them and voila ...
you have all external RB's WiFi interfaces "connected" = managable from this 433AH.

I think I didn't get your statement: *3 x WiFi interfaces as add-on cards and antennas*
Which three WiFi interfaces you are talking about?

I think I didn't get your statement: *3 x WiFi interfaces as add-on cards and antennas*
Which three WiFi interfaces you are talking about?

The ones that could fit in the 3 miniPCI slots of your RB433.
http://routerboard.com/RB433

I think I didn't get your statement: *3 x WiFi interfaces as add-on cards and antennas*
Which three WiFi interfaces you are talking about?

The ones that could fit in the 3 miniPCI slots of your RB433.
http://routerboard.com/RB433

Yes. Then I have to buy wireless cards for that slot if I don't want to use VAP interfaces.

I think I didn't get your statement: *3 x WiFi interfaces as add-on cards and antennas*
Which three WiFi interfaces you are talking about?

RB433/RB433AH has only slots for installing WiFi cards, cards like this one http://routerboard.com/R52
As you can check RB433 has 3 slots so you can install 3 x RB52. Each RB52 could work as AP therefore RB433/RB433AH could manage/work as three real APs. If you connect more WiFi interfaces - using CAPSMAN - then one RB 433/433AH could manage more APs.
As CAPSMAN can manage hundreds of interfaces then the question "how many ?" is quite irrelevant.
CAPSMAN could be even installed on RB device with no WiFi interface and manage intefaces which are physically installed in any of your Mikrotik device so you will see that your question could not be answered as Yes/No or simple 1 or 3 or 5 or any particular number.