To avoid replicating the code from the "town_center" menu (setting up guards, walkers etc.), maybe start the game with the town menu, and don't jump into a town visit mission.
So in "start_phase_3" modify "continue" to do just that:
("continue",[], "Continue...",
[
(assign, "$g_starting_town", "$current_town"),
(call_script, "script_player_arrived"),
(party_set_morale, "p_main_party", 100),
(set_encountered_party, "$current_town"),
#(call_script, "script_prepare_alley_to_fight"),
(jump_to_menu, "mnu_town"),
]),
Didn't test to see if that's enough, but it's very likely.
So in "start_phase_3" modify "continue" to do just that:
("continue",[], "Continue...",
[
(assign, "$g_starting_town", "$current_town"),
(call_script, "script_player_arrived"),
(party_set_morale, "p_main_party", 100),
(set_encountered_party, "$current_town"),
#(call_script, "script_prepare_alley_to_fight"),
(jump_to_menu, "mnu_town"),
]),
Didn't test to see if that's enough, but it's very likely.