@sorce plan sounds like a plan
Important tip:
- keep smoking but stop watching football and watch rugby instead, but cheer for France

(even if it's really not easy to cheer for the French XV these days

)
Otherwise regarding your ficus: retusa are really tough guys, you could basically do whatever you want to them and they'll survive.
They grow fast, however in England it will mainly grow during summer (does summer actually exists in England, I don't think so...

)
During winter: I don't have any specific set-up for my ficus inside during winter and they don't care.
I just put them close to a window (in order to get the most sun/light as possible) and I take care that they don't get too cold (never below 55 - 60F - approx 13 - 15C -) and don't get dry. They just grow slower. If you want you could put the pot on top of a tray/plate with water inside in order to get a more humid atmosphere but without having the base of the pot soaked in water.
Put it outside during summer, the sunnier the better. If the weather in England didn't change too much since I left Europe you shouldn't have any problem regarding the watering

If exceptionally it doesn't rain then water it, if your soil has a good drainage you shouldn't be able to over-water it.
You could layer where Sorce showed you and if the layer doesn't work (ie if there is no roots growing there) you may certainly be able to just chop it, plant the trunk in a pot and it will most certainly roots from there, the remaining part of the trunk will bud back.
If you do the 'chop, plant and wait for roots' plan you might want to prune it first in order to reduce a little bit the foliage (and get a sort of balance between: enough leaves to bring processed sap to the growing roots, not too much in order to avoid to have too many leaves to feed with a trunk with no roots). If you don't do it your ficus will most certainly do it itself by loosing the existing leaves anyway.
In fact you could chop/layer your ficus basically wherever you want and every cut will give you a new tree. Example with the much less than 50 shades of blue below:
For the picture you showed asking if it's a problem: no it's not.
It's just a 'scratch' in the bark, your tree will be fine with that however you might want to carve it in order to make it nicer (in the 'hollow part of the trunk with nice scar' department).
At one point you might want to de-pot your tree also in order to check its roots and see if you can't get a nice nebari with them.
Last point: I like the base of your tree.
For a tree that seems obviously to come from a general retailer (i.e. not a bonsai specific nursery) I find it really nice, normally these kind of mass produced retusa aren't that cute.
