The wifi signal is from your phone so not dependent on your network but the connection speed from your phone to the network will be dependant on the network signal.
You should be able to connect most devices. I have certainly not have had any problems with any of my devices. You can connec multiple devices but I can't remember the limit. The most I have ever connected myself is 2 at anytime.
One thing to note is, there are 2 versions of Joiku, the free version and the paid version. The main difference is the free version has no encryption/security which means it is an open network. While it is fine to use at home, trying to use it is a public place such as an airport will result in every mobile device searching for a open network connecting to it.
I don't have a Tab but I have had no problems with other Android devices.
I see you have downloaded the LIte version which will give you an open network so your Tab should connect pretty much automatically. Did you set up Joiku properly, i.e. did you specify the correct mobile internet access point? You also need to have Joiky running.
