Charlton signed 14 players after promotion to the Championship – with Tomer Hemed’s switch from Brighton the last to be cleared by the EFL.
That could become 15 if the Addicks can agree a deal with free agent right-back Adam Matthews.
“It was an important summer,” said head of recruitment Gallen. “We signed 14 players. I don’t want to do that again – it’s too much.
“It was just too much work, too many problems and too much hassle.
“It was important for me to get players like Tom Lockyer on a two-year contract, Ben Purrington on a three-year contract and Ben Amos on a two-year contract – and not to do what we had done previously, where we had to do everything short term.
“I had to push hard to get more commitment from players and their agents. And Roland [Duchatelet] was alright with it [handing out longer contracts].
“We got to a stage where all the talk was ‘yeah, Charlton did great in the final – but they have got no players’. That was all true. But at the back of my mind, although you are not completely in control of things, myself and Lee [Bowyer] thought we could manage.
“But looking forward 10 or 11 months, I’m not doing that again – no chance.
“Out of those 14 players it wasn’t like they were all completely new players with Ben Amos, Ben Purrington and Jonny Williams coming back.”
Replacing Lyle Taylor could be a huge task if the striker – the subject of renewed and big bids from Brentford at the end of the August window – either moves in January or leaves on a free in the summer.
“We will try to get Lyle to sign something,” said Gallen. “He wants to sign something – the main thing is it has to be financially right for him. We’ve said it has to be financially right for us as well.
“But Roland is also encouraging me to find a common ground. It is something he always asks me about.”
Gallen says his new role as a director does not change the dynamics with Bowyer.
“I would never think I am the boss,” said Gallen. “I’m maybe a bit old-school, but the manager is in charge and the rest of us are the supporting act.
“Other people might feel differently but I’m there completely to try and help him – and vice versa. It has been going well for a little while now.”