You may facing known problems.

some newer ext4 filesystems doesnt mount on maemos old kernel.
try "dmesg" after your "sudo mount loop -t ext4" and see its output.
Dont mess with /etc/fstab until you have a working solution with mount. (fstab uses mount)
Your "Chown -R user:user plus /dev" scares me.

maemo uses busybox losetup witch is missing the useful --partscan "-P" option.
So if you img contains partitions you cant do the following.
(On modern linux you can just use losetup -fP <absolute path to img> and you get all partitions like /dev/loop9p1 etc)

commands to mount a "partition image" file under maemo:
sudo gainroot
# prints first free loop device
losetup -f
# you can replace /dev/loop9 with the output from above
losetup /dev/loop9 <absolute path to img>
mount -t ext4 /dev/loop9 <path to dest mount point>
# on error watch "dmesg" !

# cleanup
umount /dev/loop9
losetup -d /dev/loop9

In the bright future maybe
"Better loop mounts with NBD"
https://fosdem.org/2019/schedule/event/nbdkit/
is coming and may allow users to get stuff done

if you have a hard drive image with partitons just boot to a more modern distro like devuan or leste on your n900.