Here is a short review/summary of the Inphonex VoIP service by NCH: http://nch.com.au/phone/sipinfo/inphonex.html
1. There is no information regarding call transfers, but for the other VoIP providers that NCH reviews, they tend to indicate if they don't support the feature.
3. There are possibilities of delays, especially if you reside outside the USA (where they host their VoIP servers). Another provider I believe that forces calls to go through their servers is CallCentric, and I also experienced long delays and quality issues with their service, but I was in Australia, so that is more understandable.
Bottomline: There is not enough information for me to accurately conclude whether Inphonex (also known as VarPhonex) is a suitable solution for you. My best advice is to actually try it out and see if it works ok. You can actually get a free account from them (although it is not so obvious when you first look at their website), by going here: http://www.inphonex.com/reg/free-voip-calls.php
The free account should give you an idea of the quality/delays you should expect for calls on their system. I am not sure however if the free account will in fact support call transfers, so you may need a paid account to confirm whether the feature is supported if you can't get it to work with the free account.