Access Point AND web client

Hello, I hope someone can point me in the right direction.
I am using nodeMCU and WeMos devices as my development environment and the Arduino IDE for programming.
I can make a device a client on an existing network and do stuff - that's all good.
I have just set a device to be an AP, I can connect my phone to it and I can turn an LED on and off - that's all good too.
What I would like to be able to do is as follows:
Have the device set up as an AP which displays a simple web page when I connect to it.
I would like to be able to scan for local wireless networks and select one OR just enter the SSID and key for a known network.
Then I would like the device to reset and for it to connect directly to that SSID with the password supplied and then just let it do stuff.
I am at a bit of a loss - mostly because of my lack of knowledge I am sure.
I read that the 8266 can be both AP and client at the same time - is that right? If so, is it actually a question of inputting the SSID and key from a web page and storing them in variables which are then used by the client side to access whatever WiFi network as specified and then let do whatever I wanted it to do at that point?

In the example I used that set up as an AP, the main loop looks like this:

void loop() {
server.handleClient();
}

Can I just insert my code for doing whatever I want the client to do withing this loop?
How do I get it to connect to the AP that I specify when filling out fields on the web page that specify the desired WiFi network?
I am struggling to grasp the basics I feel, could anyone point me in the right direction?
Am I the only person who has tried to achieve this (I suspect and hope not!)

Thank you for your help.
Kind regards
Richard