Spaniard Perez, 27, scored 17 goals in 37 games last season and was close to joining Everton before the Gunners met his 20m euro (£17.1m) release clause.
Germany international Mustafi, 24, signed for a fee in excess of £35m.
Jack Wilshere could also be going out on loan this week, with reports that Crystal Palace and Bournemouth are both interested in the England midfielder.
Perez and World Cup winner Mustafi join recent signings Granit Xhaka, Rob Holding, Takuma Asano and Kelechi Nwakali at the Gunners.
“He’s not only a goalscorer, he’s a guy who combines well with partners, who can give a final ball and makes good runs,” said Wenger of Perez.
“He’s got a good eye for goal and had an outstanding season last year.”
Speaking about Mustafi, Wenger added: “He is at the right age. He has good experience.
“He is a very focused player who can play with the ball as well. We have taken a great player but have prepared well for the future.”
Meanwhile, Werder Bremen are hopeful of signing Arsenal midfielder Serge Gnabry and say the transfer could be confirmed on Wednesday morning.
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