Home Networking

I have built and am using a home network. It consists of a Huawei hg659b router/modem supplied by Vodafone, New Zealand, 2 desktop computers (complete with printers) in a wired network and a laptop and a 9" tablet connected wirelessly.
The details of the hardware in the home network are as follows:
Acer all-in-one using an AMD E1-2500 APU with 4Gb RAM and a Dell 2400 Dimension using 2.4Ghz CPU with 2Gb RAM. The printers are both monochrome laser printers. HP laptop with similar hardware as the Acer all-in-one.
Now I have started to build a wired network in my workshop. At the moment it has 3 desktop computers but I am planning on making it larger (up to 4 more desktop computers). All the pcs in the workshop are using 2.4GHz or 2.8Ghz CPUs with 2Gb or 4Gb RAM with various video cards and hdds and cd and dvd burners.
The possibility of connecting the two networks together is appealing.
Connecting the "house" network to the "workshop" network via a cable is not possible. I do not have access for the cable either overhead or underground. Power line adapters also are not an option.
Now here is where I am running into problems.

As I see it I have two options:

Firstly, put a wireless ethernet card in one of the "workshop" pcs and network everything else to that. I don't mind leaving this pc on all the time as it will also be used as a hardware testbed machine.
The problem with that idea is that the HG659b signal received in the "workshop" is about -90db, as measured by an android mounted wifi signal meter. This probably is not strong enough for a viable connection but I am willing to be corrected on that point.

Secondly, use a modem as an AP.
At the moment I am looking at this option as the level of signal received from the HG659b should be large enough for the WAP to work.
I am using an Rta1025w modem at the moment but I have a Netcomm NB6Plus4 which I might use if the Rta1025w does not work sufficiently well. Outside the workshop the signal increases to about -60db or -50db. So with that information I am looking at using the RTA1025w with a directional reflector fitted. I am prepared to mount the RTA1025w outside the wall of the workshop to improve the 'received' signal strength. When I am back inside the house the wifi meter 'sees' the Rta1025w quite well (as it is still set up as a modem).
What I want to do is set it up as an AP. I have been told that this is also called wifi client mode.
How do I do that?
I am assuming that I will need to connect the rta to a pc and phone line and change its settings online but can I do that using a pc that is already networked using the hg659b. In other words will using the pc with the second modem (RTA1025w) corrupt the settings (stored in the pc) of the first modem or do I need to use a third pc for the RTA1025w.

Any help (or criticism) would be greatly appreciated.

 

I would run the whole setup under a secure WiFi command.
Use WiFi extenders to boost the network range under a separate SSID to help mobile devices in roaming around the network.
I love the Alfa USB range of external NIC's as they seem to run superbly with Linux, and can go dual band/Monitor mode/Injection support!

Dual 8dbi receivers run a good distance with one or two walls.

 

Make a wireless bridge, that would give you wire connections to the other end. Here is an example..https://wiki.dd-wrt.com/wiki/index.php/Wireless_Bridge.
You could use outdoor antennas for the bridge signal.