Now I have BRM confidently under control I have been assessing my game in an attempt to determine the next priority to focus my attention on.

I've been studying up on learning recently in an attempt to become more efficient in my poker training. The following passage which I read while reading about learning recently helped me realise that one tabling is the only sensible way forward for me for now (my bold) : -

The point of learning, when the impossible becomes possible, occurs at the junction of consciously changing our actions and responses ... we need to go through the necessary skill development process very, very slowly so that we can consciously control our thoughts and actions to create the new responses and achieve the formerly, personally impossible result ... If we can do something a little bit faster and still do it correctly then we can repeat it again only even faster ... The skill learning process has not yet finished as we then need to repeat the newly learned processes for as many times as it takes until we no longer have to consciously think about the process. At that point we have thoroughly learnt something and it has become a part of us. Further practice then refines the performance of the skill.
I may lose some speed in the bankroll climb, but I think it will be compensated for by grooving the right processes into habits at the table, and the reduced risk of spew when/if I tilt or just generally start playing sub optimally. Getting the right habits formed and internalised is essential in this early phase of my poker development so that in itself would make the one tabling a very worthwhile consideration. However the reduced risk of spew is also very worthwhile in itself, I say this because I have isolated where I came unstuck in my last attempt to develop a bankroll. Once I had a bad beat and made the odd bad play on one table it cascaded onto my other tables and before I knew it I was playing sub optimally (of course that's relative, I'm no where near an objective optimum, but personally sub obtimally) on 8 tables which accounted for about 40% of my BR at the time. If I had been one tabling I'm fairly sure I would have noticed this after losing the buy-in, or surely, by the time I would have opened another table and done the same thing. With 8 tables open at the same time - I'm exposing myself to 8 times the risk in these situations.

Once I have good habits / 'natural instinct' then I can add a few more tables.

Also the following has forced me to re-evaluate my focus at the table: -

The great problem of most people when they learn new skills is that they spend most of their time repeating the easy stuff ... but they cannot progress overall because they do not tackle the things that remain impossible for them. These impossible things naturally feel very difficult to do but through following a sensible method they become possible. To supercharge our learning we must put most of our focus upon these difficult to do things.
By multi-tabling I was avoiding one of the things I find hardest to do and that is to put my opponents on a fairly accurate hand range and consequently develop good reads on the villian. Now that I'm fully aware of this I realise even more why it is important for me to focus on one table for now, aside from getting the very basics of (1)preflop positionaly aware play, and (2)post flop bet sizing, on auto pilot - one tabling will also allow me to become more adept at (3)ranging and reading the villian.