Extending the network for internet with broadband using Homeplugs / BT Mini WiFi Home Hotspot

[#1]

I already have a BT Mini WiFi Home Hotspot extender with one WiFi Hotspot.  I badly need at least a second, but I have a number of questions and would be most grateful for any answers in principle :

1. Can I extend the network with an additional (second) WiFi Hotspot, using the same BT Extender ?

2. How many WiFi Hotspots can be added ?

3. Can you buy just the WiFi Hotspot without the Extender to use on the existing network ?  In which case, where as I am having difficulty finding just another one ?

4. Are other makes compatible with BT - for instance would a TP Link WiFi Hotspot work on a BT Mini WiFi Home Hotspot extender ?

All I can find is complete new systems on eBay for instance.  I have seen a couple of TP Link WiFi Hotspots without the Extender, though.

My problem is a long house (formerly three cottages) with very thick walls and rooms like a train - you go from one into the next into the next ....  Getting WiFi signals to all the rooms is impossible without an Extender, and installing an ethernet is really not practical because it means knocking holes in the attic through the thick walls with very little head-room !  I could run the cable externally but it would be ugly.  My office is in a separate building outside on the same electricity circuit, but running a cable underneath the tarmac drive would be equally impractical.  The only solution is WiFi Home Hotspots in reality but what are the limitations ?

Thanks for any comments.

[#2]

Sorry, can't help with the WiFi extenders - I use a redundant router connected via a  powerline ethernet link to stretch my wireless.

Why not use a wired powerline solution - at least for the office. The performance will be better.

[#3]

Thanks for the suggestion.  Presumably by "powerline ethernet link" you are referring to a physical cable, otherwise I am not sure what you mean.

Actually, within the house, I already use two remote WiFi routers, connected in one case by an ethernet cable direct from the master router, and in the other case by a Home Plug, which gives me about 70% coverage.  Ideally I would like to cover the rest of the house and also be able to access the internet from the office.  The two obvious solutions are either to dig a trench for an ethernet cable running under the tarmac, or to have a new telephone line installed by BT just to serve the office with broadband.  Neither solution appeal to me for obvious reasons.

That is why I am thinking of more Home Plugs or equivalent, which, though probably not ideal, would in fact work adequately in the office, as I have tried it already using the one existing Home Plug which I use in the house for the remote router.  Hence my interest in buying more Home Plugs, but I do not know if they are all compatible with one another.

[#4]

Having just "Googled" for "powerline ethernet", I realise now that powerline ethernet and Home Plugs / BT Mini WiFi Home Hotspot are all one and the same thing !