1-3 Last I tried obarun-install on a machine at work, although the installation was complete, asked for user and root passwords, 66 was left without trees or services. It was all blank, user and root.
I suspect the cause was a faulty efi installation, which with win10 the totality of efi - wiki is useless. I don't have the liberty to remove win10 from the machine, boot is 100mb and it is not vfat, it is fat32, the wiki calls for a 500MB boot.
1-3 Even though you remove the syslinux choice the installer keeps trying to install syslinux, the reason being it is on the lists 2-3 times, so you can't escape installing the crappy abandoned for 10y software. But this is an old issue with obarun and it is a choice enforced by the dev.
4 This is a dangerous thing to do, having auto update/upgrade.
a script with
% sudo pacman -Suy --noconfirm
will do what you want but eventually it may break your system and you wouldn't be able to know why, unless you hunt into /var/log/pacman.log
To run this from X you need something like gksu or doas, otherwise if sudo is not open without password check there will be no notification on X asking for pw. On console/terminal use sudo.
% gksudo pacman -Suy --noconfirm
Again this is not advisable, especially when obarun is based on two distributions for which obarun doesn't have ultimate control.