quinnfyre, if I had to do it I would consider a glass jar, with both plant and jar on a sponge base. This way, I could observe what is going while keeping the plant in a 'terrarium-like' environment.

Hi Quinnfire. Great question. Since most of my rooms are filled, it's a difficult task.
When a new plant is brought in I set it/them on an end table, about 5' from a south window.
Since our biggest fears are insects and diseases, it's important to first inspect all parts of the plant..Upper, lower leaves, stems, trunk.
After inspection, each plant is taken the sink, washed with dishsoap then rinsed with plain water.
After air-drying, the plant/s go on the end table. Though I must admit, the end table is not from from older plants, but I simply do not have an isolation room/spot.
Plants are kept on the table 3-5 days, (inspected daily) then go in a spot they'll live permanently. BTW, most of the time, they live in the pots shipped in, (depending on size, etc) from weeks to a couple months.
Are you having an isolation problem? Toni

Not really a problem, exactly. It's just that I got some new plants, and I feel I ought to isolate them, but it's hard to decide where and how. I've been known to just add them to the shelves anyway, but mainly on the left set of shelves, which houses my succulent collection, because quite frankly, they're easier to replace than my AV and orchid collection. Right now, my newbies are on my desk, getting in my way. The only plants on my desk are a bunch of AV babies which are encased in plastic baggies, so they're safe. I considered that option, but unless I know a plant likes that much humidity and nonmoving air, I try not to put it in a bag, to avoid rotting.

I did give the newbies a cleaning, and a wipedown with neem, which hopefully should help with potential critters. I'm mainly worried about critters, really. Well, we'll see how it goes. At this rate, it may not matter shortly... I'm just about out of room for new additions anyway.

Quinnfyre, to be honest, when I buy a plant, it goes on the end table, but the table only holds so many. If there's no room, after inspection and cleaning, plants are set with older plants. Mostly succulents.
I got scared a couple wks back. I thought one succulent had mealy. The plant been around since last Nov. Suddenly there's white gook. I swiped rubbing alcohol over the leaves, kept separated 3 days, and prayed..so far nothing, but there's always a chance.
One problem is eggs hide in places we don't see..As soon as a certain temp hits, eggs hatch. It can takes months before they spying them. So, unless an insect is obvious, what is the appropriate time to keep a plant isolated? 3 months, 6, a year?
If there's room, isolate, if not, we have to take the chance.