With a lovely big run of about 24 square metres, you could have up to a dozen hens, though it would be better to start with fewer, give them space, and get used to keeping them through your first winter. Then, if you wanted more and could cope with all those eggs, you could add younger hens gradually, so you got a flock of mixed ages rather than a group where at some point they all got old at the same time.
Lots of advantages to plastic - easy to wash, wipe dry with an old towel, great in winter especially when the hens mustn't go back into a damp coop at night. Redmite less likely, fewer nooks and crannies, coop should be easy to dismantle and scrub all the edges etc if necessary. Never any need for creosote, which is messy, toxic and takes up to 3 weeks to dry, necessitating a spare coop for the hens whilst the fumes go off. good-quality plastic will last for ever, to all intents and purposes, compared with wood, so your coop will keep a good resale value - nobody wants a second-hand wooden one, possibly with integral redmite, difficult to dismantle and transport. So you want to get it right from the start - as i said, research what design features are needed, and the right size of coop for your birds. If you decide to get another coop, keep the wooden one if you can, it will be very useful when you need to introduce new birds as you can quarantine them in it, or let young ones grow on until old enough to join the flock, dividing the run with netting to keep them separate. Maybe cover it with a tarp when not in use to keep it dry and clean.
As you'll gather, i'm a big fan of plastic coops, I'm very happy with my Green Frog, and the design of this one has improved in the past year since I got mine. The more modern ones are coming down in price as production increases, (Omlet is still very expensive and in my opinion not the best for the money) and I really think they are the future for chicken keeping, at least on a domestic scale.