With my tremendous experience of two pigs...
But as a newbie myself, you might like to know my perspectives.
I bought two OSB gilts, intending to breed, last August. We decided not to breed from the one and she went in January. The other has just had her first litter.
At the beginning they shared a big oil drum as a bed. They soon outgrew that (maybe two weeks), but continued to sleep in a cobbled-together-from-pallets-etc bed the size you describe for another couple of months. In fact, they slept together in a space this size, but open on two sides (like an L) and indoors so not needing to protect them from weather, until Gaby went away (at 7 months old.) By then you could see that Meg was pleased to not be sharing that bed space any longer.
By October we had arranged to get a secondhand 9' x 7' ark. It seemed absurdly huge, I was even worried it would be so overlarge they'd be cold in the cavernous space, and was certainly worried they'd poo and pee in it as well as sleep in (less than half of) it.
The ark finally arrived in March (long story...), and still seemed ludicrously large for Meg (now 10 months old.) She liked it at first but didn't like the water coming up from the ground, so carried on sleeping in the chicken house we'd put at her disposal while we waited for the ark to appear. The calves who shared the field with her thought the ark was great and they used it, which was good as I didn't like them going in the chicken shed with Meg...
(Because calves aren't careful about being clean in their bedrooms, being the main reason I didn't like them sleeping with Meg.)
I finally managed to get the ark floored in time for my now heavily pregnant gilt to move in at the beginning of September. It no longer seemed over large at all, in fact I began to wonder whether it would be big enough if she had a large litter and felt that if I installed farrowing rails along one (long) side she would not be comfortable turning around widthways.
Thankfully she's just had 5 beautiful Saddleback x piglets, and the family has ample room in the ark (which BH describes as the Pig Palace.) But no way is it over-large for one OSB sow and her litter. Any smaller and you could see that avoiding the babies (especially if there were more of them) when lying down would be very difficult. I am glad I have not had to install farrowing rails along the long side - she is very very careful to find them all and warn them before she lies down, but I think if she had 12 or so, it would not be surprising if one got squished in the first day or so, while they learn how to listen to Mum. So for her next litter I am thinking maybe I would try somehow to put farrowing rails across the top (short side) so there is still plenty of room for her to mooch about and lie down any way she chooses.
How exciting to be starting your adventures with pigs this weekend!
Please tell us all about it - and of course let us see some pggie piccies