Hello,
Well i think as you said that you thinking of doing your garden up as it has been un touched... well i think as you start sorting it out you may start to reduce some of the critters as there will be less shady spots for them to hide.
Prehaps you could start to encourage the birds etc as some of them will eat the snails.
Even get your self a couple of hedgehogs as they love slugs and snails!!