I used an excel log till last year and now I am using a 24-week training plan (with Training Peaks premium) for climbs in Ecuador end of this year (not sure if it will happen). Based on my experience, I would recommend using a training plan. If you plan to use this plan multiple times over the next few years, I think it is worth the one-time cost.
Also, a training plan takes out the guesswork and gives you clear direction on what needs to be done. As a beginner, this is very valuable to me. Here is an example of the detailed instruction for my long AeT run/hike (towards end of transition phase):
Run/Hike on hilly terrain, vert gain min of 2,000ft
If you train outside the duration of the workout should be total time out. That includes the time both up and down. For example: A workout with a 2hr duration would be the total time from start to finish. This also includes if you are hiking up stairs in a building and back down. If you take the elevator down seen description below.
If you are using an alternative methods like a treadmill, stair master or hiking stairs(taking elevator down) the duration of the workout would be for the time hiking uphill. If you have a 2hr duration workout that would mean hiking on a treadmill for 2hrs.
If you are combining this with a Training Peaks premium account, there are added benefits of tracking metrics over a period of time.
Maybe others who are using Excel Logs can provide some input.
I hope this is helpful.