```python
from pyaedt import Edb
from pyaedt import Q3d
import os
import tempfile

# Setup project files and paths
aedt_temp_dir = tempfile.mkdtemp()
project_name = "your_project_name"
edb_project_file = "your_project_file.aedb"
edb_project_path = os.path.join(aedt_temp_dir, project_name, edb_project_file)

# Download specific project file to temporary directory
# Assuming a function `download_project_file(url, dest_path)` is defined elsewhere to handle the download
url = "http://example.com/your_project_file.aedb"
download_project_file(url, edb_project_path)

# Open an EDB project
edb = Edb(edb_project_path, project_name, True)

# Create a cutout on selected nets and export it to Q3D
selected_nets = ["GND", "VCC"]
cutout_name = "cutout_for_q3d"
edb.core_nets.create_cutout(selected_nets, cutout_name)
edb.export_to_q3d(os.path.join(aedt_temp_dir, cutout_name + ".aedb"))

# Identify pin locations on the components to define where to assign sources and sinks for Q3D
# This is a simplified representation. Actual implementation may require accessing the layout and components
pin_locations = {"U1": {"pin1": (0, 0, 0), "pin2": (1, 0, 0)},
                 "U2": {"pin1": (2, 0, 0), "pin2": (3, 0, 0)}}

# Append Z elevation to pin locations (assuming a function `append_z_elevation(pin_locations)` is defined elsewhere)
append_z_elevation(pin_locations)

# Save and close the EDB
edb.save_edb()
edb.close_edb()

# Open in Hfss 3D Layout and generate the 3D model
hfss_3d_layout = edb.core_hfss.Hfss3dLayout(edb_project_path)
hfss_3d_layout.create_3d_layout()

# Export the layout to Q3D
hfss_3d_layout.export_to_q3d(os.path.join(aedt_temp_dir, project_name + "_3D_Layout.aedb"))

# Launch the newly created Q3D project
q3d_project_path = os.path.join(aedt_temp_dir, project_name + "_3D_Layout.aedb")
q3d = Q3d(q3d_project_path, specified_version="2021.2")

# Plot it
q3d.plot(show=False)

# Assign sources and sinks on nets using the previously calculated positions
# This is a simplified representation. Actual implementation may require creating ports and assigning excitations
for component, pins in pin_locations.items():
    for pin_name, position in pins.items():
        q3d.modeler.create_port_between_pin_and_layer(component, pin_name, "TOP", position)

# Create a setup and a frequency sweep from DC to 2GHz
setup_name = "Setup1"
q3d.create_setup(setup_name)
q3d.create_linear_count_sweep(setup_name, "GHz", 0, 2, 1000)

# Analyze the project
q3d.analyze_all()

# Compute ACL and ACR solutions, plot them
# Assuming functions `compute_acl(solution)` and `compute_acr(solution)` are defined elsewhere
# and similarly for plotting
solution = q3d.get_solution_data()
acl = compute_acl(solution)
acr = compute_acr(solution)
plot_acl(acl)
plot_acr(acr)

# Release the desktop
q3d.release_desktop()
```