Little improvement in starting a vm. In my system a iptables command without the flag -n takes alot of time, eg: iptables -vL FORWARD takes 10.171s, while iptables -vL FORWARD -n takes 0.022s. I'm not aware if this is common, or just a weird problem in my system. Anyway, the use of that flag in some point of your scripts (eg manage_tuntap) may be worth.