Refer to page 187 in TftNA. Take your average weekly hours for your most recently completed training cycle. Say you averaged 10 hours/week for 30 weeks. Start week 1 of the Transition period at 5 hours. The evaluate the rates of increase in weakly volume from last year. With notes you made and with the grades yo gave to the workouts you did you can suss out what is a reasonable increase in hours/week for you. Say you bumped hours 10%/week for a couple of weeks but then noticed that in the 3rd week you became especially tired. It is possible (this is why copious notes in a log are so helpful) that 10% was too much and 5% is a sager bet.
As for overall volume increase: Usually newcomers to training can make much bigger annual jumps in training volume than seasoned athletes. This is because the beginner has much farther to go before reaching his or her limits. Very high level athletes with many years of structured training may not increase volume at all. They may only tweak intensity and types of training. Where as less experienced may be able to jump 20% in overall volume in one year. There is no hard and fast rule for this and it needs to be based on how you handled this years training load. If the biggest weeks this year really taxed you in terms of energy and available time then that may be you peak hours possible. But maybe you can hit those peak hours in more weeks spread through the end of the base period. Which will increase your yearly volume and by extension your base fitness.