I tried to start something along these a few years ago, but it didn't really gain much traction, so good work on attempting to start something up again here Chris. I may well join you at some point, even if isn't for the entire duration of the year.
Regarding my purchase related activities, I largely took an absence of this hobby for a year or so, largely down to growing a beard! Since shaving it off I have been enjoying buying some new bits and pieces, and I started keeping a spreadsheet to document the gear I use (yes I know, it's an OCD thing for sure), and having it a look at it, made me well aware even though I have a lot of hardware/software, I seem to focus on a few time tested staples more than others. Which made me question, why do I continue to buy items which are most likely to be overlooked in favour of ones I am more likely to use. I sometimes question whether I am walking the fine line between an enthusiast or a hoarder!
I remember we had a discussion around then that often buying new gear was sometimes not about needing something, but down to other factors.
In keeping with the theme of restraint threads, I've noticed 'other' shaving forums sometimes have participation threads like 'Decemboar' (eg a focus on using boar brushes for the calendar month of December). They can be a great way to keep an interest in the hobby without buying new gear.
One last point, I recall from the B&B ones, the participation threads for not buying any gear, they have a few rules/exemption clauses, which may or may not be of interest, but if they are they might be worth looking out for. I recall, a few of the exemption clauses include if you have one brush or bottle of witch hazel or something, if it breaks or it if you finish it you are allowed to replace, or being allowed to still participate if you are gifted something.
Anyway, sorry if I rambled on and good luck to those who choose to participate in this noble project!