I'll second what Mr Fakename has said.
The Bellina will grow twice the size of that box so will soon outgrow its space.
The best solution is a 30x30x30 cm polystyrene fish box available on ebay - second hand they are not too expensive. You can leave the lid on with a slight gap. Like this I can heat the inside 10 degrees C warmer than the outside using only 2 watts of power. With no insulation it would be in the region of 20 watts.
A plexi glass tank would probably need 10 watts. If you add a fan like you are suggesting it will be 18 watts as the fan will blow most the heat out.
The only big problem with a polystyrene box is lighting, there are mini led's available that would suit such a box but depends where you live whether you can source the right light.
I can highly recommend an adjustable heat mat, otherwise you will need a thermostat to regulate it.
You will also need a timer to turn it off at night.
If you grow on a heat mat you will soon find that your plant drying out from the heat will be your main concern. Ventilation will just speed up the rate of drying and once you have it all set up (with a heat mat) you won't want any ventilation, certainly not for only one plant - you won't need it. But it is always good to have a spare computer fan on hand if you do think that you need it. If it gets too humid or the substrate doesn't dry out fast enough (I would still recommend a faster drying media over a fan or opening the lid more but a fan should of course be used if it is needed) I'm just saying from experience I doubt you will feel that you will need a fan with only one plant - the air current the heating of the heat mat will create (heat rises so heat creates air flow) and a gap in the lid.
But as a ps: If you read this aricle here you will find this grower keeps his Bellina at 14 degrees C in winter
Advanced Phalaenopsis Care: Summer vs Winter Blooming Phals >> Here But Not
I have not tried this low myself but 29 degrees is way too hot for a bellina, 24-25 degrees C during the day and 20 degrees C at night is the general guideline but it seems the plant might be able to handle colder.