So pleased I was able to offer you a bit of hope and direction.
When my outbreak started, like most people, I hadn't heard of Marek's and didn't know anything about it.
I let the chickens out one morning a year gone Sept and one of my young pullets was hobbling badly.... basically walking on her hock. I naively assumed it was an injury but a day or two later a second one was badly lame. Both had been fine the previous day. Then the third one went down almost in front of me a couple of days after and was lying in classic Marek's splits position, having been normal a couple of hours earlier. By then I had done my research and was feeling pretty alarmed. Most of the advice I read initially was to cull the whole flock... I had about 30 chickens!!
Then I started to read threads on this forum where people were battling the disease and trying different remedies and it gave me hope, so it's wonderful for me to be able to pass that on to you, especially as I can now speak from experience and say that things don't always turn out to be nearly as bad as a lot of what you read.
The first pullet I think was the one that learned to hop after a few weeks of tripping and flapping and floundering. The second one deteriorated over the next few days and was unable to stand or walk at all. Then her neck twisted as well and she couldn't manage to eat and drink or even stay lying on her side and was rolling over onto her back after I had left her propped up. I made the difficult decision to cull her (at the age of 50 she was the first creature I had deliberately killed and I cried buckets!) I did however, do a DIY post mortem exam and found two huge tumours... one on her leg and the other on her abdomen... and that was enough to convince me that a) I had done the right thing in euthanizing her and b) it was definitely Marek's
The third one, made two miraculous recoveries from 2 attacks several months apart. The fourth one was a cockerel who floundered for a couple of days and then got progressively better until a fortnight or so later, was fully fit, but went on to have another attack a year later and declined that time and I had to cull. Another cockerel had a few days of lameness and then got over it and is still fine a year and a bit later.
Autumn/winter time seems to be the prime time for an outbreak, whether that is an environmental factor or just that the previous spring/summer's chicks are reaching that vulnerable age, I'm not sure. It also coincides with the young cockerels starting to be at the mercy of raging hormones and the pullets and hens being harassed by them as a result. Stress is definitely a trigger. If you have any young cockerels, removing them to a bachelor pad will help alleviate that stressor for both sexes.... but for me the girls wellbeing is my main priority, as surplus cockerels are just destined to become dinner.
The aggressiveness of the virus is more about how many birds it affects and the fatality rate rather than how it first exhibits. I certainly can't claim that I coddle my birds. I'm not scrupulous about cleanliness and I'm not a fan of using antibiotics unless absolutely essential so I let ailments like IB run their course without treatment, It is therefore not down to any good husbandry on my part that my chickens/flock are mostly surviving with this disease when others are losing whole hatches. The only conclusion I can draw is that there is a variance in virulence of the strain and I count myself fortunate that mine is mild.
I do however think that broody reared chicks are more robust and free ranging allows them a more natural and varied diet and lifestyle, which also has to reflect on their immune system and overall ability to fight and recover from illness.
The area under your table sounds like a good place for an infirmary although I have to say that having it up off the ground makes cleaning it and tending them a little easier on the back! You might also want to do some research on chicken slings so that you can support any future sufferers in an upright position if they are unable to stand.