My flat is 17C most of the year, so I am probably not the right person to be storing anything for a decade.
Eating first sounds obvious now that somebody has said it out loud.
Some memories are also genuinely context dependent. If you learned it at a desk in winter and met it again on your phone on a bus, you can miss something you would have got at home. Not a scheduling fault.
Rule of thumb, nine or ten reviews per new card per day at steady state, more if your Again rate is high. Measure your own after a month.
Lower the new cards. Splitting decks does not reduce work, it changes which work you see first, and the cards you park in another subdeck still come due - they pile up silently and ambush you in week three.
With 45 minutes and no Friday, 10 to 12 new a day is about the honest ceiling. Ten new cards settles at roughly 90 to 110 reviews a day, which is where you should be. If you genuinely need chapter focus for an exam, use a filtered deck for that material and leave the main scheduling alone.
Descale the new kettle before you test anything, unless it is genuinely brand new.
Nine days of no new cards costs you about 200 cards you would have added. Nine weeks of a permanently scary queue costs you the habit. Take the smaller loss.
Do not reset anything. Set new cards per day to 0, set a maximum reviews per day you can actually finish - 120 is about right for 40 minutes if your cards are small - and sort the backlog oldest first instead of random.
The reason the number only dropped by 60 is that the cards you failed came straight back the same session. That stops once the genuinely leeched cards are flushed out, usually in the first three days. A mature card that was due 16 days ago is still mostly intact; two weeks of overdue on a 45 day interval is noise, and you will pass most of them and push them back out past a month. My last 900 card backlog took nine days at 120 a day.
Check how many of those 250 are repeats within the same session. If your Again rate is 30 percent you are really doing 320 reviews to clear 250 cards. Lowering new cards for a fortnight brings the Again rate down and the session shortens on its own.
Whatever you buy, buy one you would not be devastated to break in a shared kitchen.