what is the recommended character speed for a beginner?
The best speed for YOU depends how good you are - in the sense of aptitude.
You might be able to start at 25/25 and pick it all up in 3 weeks.
You might be grinding along for a year at 10/2 just to get through.
The thing is - you won't know until you've tried - and we can't tell you because we only know what you tell us.
The first exercises can be a bit of a shock.
There are a number of pit-falls to avoid.
If you can't touch type already, beware of forming a link between morse and key-press - else you may have a job getting away from the keyboard to decoding in your head.
The move on point is 90% right in an exercise - but if it's only in short term memory and hasn't sunk in, you may find you stall at exercise 10 or so when it starts to fade, and you then have to start again.
Make sure you are making progress and not just working away at the same exercise for weeks on end else you will lose interest and give up like maybe 90% of starters.
That's the reason for slowing the code - to make it easier. Aim to get through all the 40 exercises in a few month at least and then think about speeding up, - but if you make progress at 25/25 or 20/20 or 15/15 then stick with that.
Make sure you choose an audio frequency at which you ears can distinguish the morse. If you can't hear it easily you won't decode it easily.
This is often not a problem - but maybe older ears or too much loud music . . .
Only you can judge how well you are progressing . ..