Watering & ventilating in terrarium

[Froggle]

Wondering if those of you more experienced might share your knowledge on achieving good ventilation & setting up automatic watering systems in terrarium.

1. Ventilation - My Terrarium is a 3ft x2ft x2ft glass tank. I have exchanged the glass lids for x4 flyscreen lids which span the top of the tank. I'm assuming to grow happy orchids in this tank I'll also need to install a fan. Could you recommend how many fans you would recommend for this set up & if more than one is required, is it best to install these so they are together & blow the air in one direction or on opposite sides of the tank?

2. Watering - Thus far I've been using a spray bottle but I'd like to install an automatic system. I'd love some guidance on what key factors I should consider in such a system. I'm aware it is best to water in the morning so that plants have the remainder of the day to dry out. I'm aware that with phals it is important not to let water collect between the leaves in the crown but I'm wondering is this the same for other types of epiphytic & lithiophytic plants? Is it vital that such a system deliver 'mist' only or are larger droplets ok?

* I should add that I plan to mount or plant directly into the substrate (sphagnum moss over egg crate) rather than keeping plants in pots.

Many thanks in advance for sharing your knowledge!!