Telephony needs

I need a portable telephone system ISDN or Analog for my Workshop (1 phone & 1 fax line) as well as my home which has 1 phone line..

2 Employees are Currently working for me, with maybe a 3'rd in future- no more planned.
Telecom has installed a Santis ISDN box with a telephone line, fax line and 3'rd number.
Currently my premises have a Office with a Analog phone, Fax and PC using 64k ISDN.
Then I have a 200m2 Hall that comprises of 100 m2 storage space and a dedicated work pit plus area left over for storing/working on cars. Here my employees have a Analog Cordless phone so they can talk to a customer while looking for parts/working on vehicles.
I have a separate Dyno room, to test the vehicles power output on the rear wheels (noisy environment).
 
I practically do everything myself and herein lies the problem.
I spend so much time on the phone that I can't get down to work.
 
Do you know who has got a few options for me (hard & soft) ?
 
Without confusing you, I thought of getting 2 or 3 of those Tiny Gigasets.
I need a Headphone/speaker unit that I can comfortably wear 9 Hours a day, it must also work in a noisy environment since I am hearing impaired. I don't necessarily need to phone out from that, but would be nice to page my colleagues.
My 1 Colleague would need a portable phone to contact him by.
It would be nice to retain a corded phone in my Office and workshop so it can be utilised by whoever is near.
 
Now for my software requirements:
It would to be able to use the Call Line Identification capabilities of ISDN in such a way that it shows me who is calling (could use my outlook database) and for me to fill in those records.
When a call comes in it would be nice to have a Synthetic Secretary take that call (so my time does not get wasted unnecessarily). Or even better cal hunting facilities.
Also when I test Cars on the Dyno (20 minutes at a time) I cannot take calls.
So callers must be given various options amongst; leaving a message, speaking to my Colleague, holding.
If a call does come thru on my hands free, I must know whether it is from outside or a colleague paging me. Then I must also have the option of; putting the customer on hold, rejecting the call or taking it.
 
I hope to have expressed myself reasonably clearly.
This was not supposed to be a brief, but more some ideas what I would like.
 
The most important functions are:
Call comes in with CLI (on preferably not only number but also name from database) then I can transfer and page the other handsets.
Preferably I don't want all handsets to ring or whether but stagger that in order of importance (Hunting).
Or Auto attendant
Answering machine function is not that important as I have a stand alone unit.
The unit must be relatively robust.
Headphone, I  don't NEED one, but it sure would be nice.
But I have realised that I probably need no PABX.