Thinking back, I recall having done a hike with my husband at the park without a guide so I went back on the site to check.
I can confirm, NOT all the itineraries require a guide! This one doesn't, for example:
parco-maremma.it
or these two
parco-maremma.it
parco-maremma.it
It would seem it depends on the itinerary, take a look at all of the ones they have on foot here:
parco-maremma.it
Some routes say that only groups that are bigger than 20 people need to book a guide, so that means they allow families and couples to enter without one.
This is not typical wherever you go, it is just how the Parco dell'Uccellina does things. I've only run across it at places that are protected habitats, such as the Uccellina park and the Massacciucoli lake near Lucca. I think that since this park is big, there are areas within that are protected and those are the ones that require a guide. You cannot go out of the routes they have set out. The beach on the inside of the park is actually beautiful - you head to Marina di Alberese, park there and then walk south along the beach as far as you want. All free sandy beach, most people stop closest to the parking lot so the further away you walk down the less crowds.
Everywhere else we've hiked we've just had to get hiking maps - there are lots of marked CAI hiking trails across all of Tuscany (red and white markings) - and just gone on our own. But in that case also getting a book with recommended itineraries is useful, so you know whether you can do a ring hike or have to go out and back. How much Italian do you speak? the better guides are in Italian, and by guides here I mean paper book ones
I understand feeling overwhelmed, there is a lot of choice across all of Tuscany! If your writing workshop goes well, you will be back, right? Take pressure off yourself and think you will come back to Tuscany, so you can choose either one and plan to visit the other the next time
Some considerations to help choose: Pistoia is closer to Florence so you could choose Lucca/Pistoia this time and save Maremma for the future. Pistoia is below the Appenines so hiking means going up in elevation, thus cooler temps in summer. From Lucca you can also head north in to the Garfagnana valley and there is lots of hiking there as well in the Apuan Alps. We've done this one a few times:
https://www.discovertuscany.com/hiking-in-tuscany/monteforato-trekking.html adding in a visit to the Wind Caves, a stop at the Ponte del Diavolo, a visit to Barga. We've stayed in Gallicano and Barga on two separate occasions to focus on the area.
Another off the beaten area is the Lunigiana, at the north end of the Apuan Alps, so you can also head to Aulla and explore that area, including hikes into the mountains.
The beauty of Tuscany is that there is lots on offer across the region, packed in into a small space overall and every single time you visit you can explore a new place and not feel like you're seeing the same thing! I also love the outdoors and hiking so for the end of June, maybe my personal choice would be Lucca/Pistoia as it is higher elevation than Maremma and thus should offer cooler days. Whatever you choose, I don't think you'll go wrong. The problem will be that 5 days will fly by and you might not even get in all that you would like
