Most people with children would want access to a swimming pool and play facilities, and actively seek out holiday accommodation that provides this- if you don't provide it families will probably avoid you anyway.
I'd think very very seriously about the dogs. Have I understood correctly that there are 2 adjoining properties? Could you make one cottage dog free and allow dogs in the other? If you do allow dogs I think you need to delineate a tiled area e.g. kitchen, utility that they have access to, and don't allow dogs on upholstery or in bedrooms - if there is space for a reading room, you might find that you can arrange the layout to accommodate a dog area whilst the building work is ongoing. Given that your target market could be wildlife enthusiasts/ walkers/ possibly surfers? in Pembrokeshire, it would be useful to have a utility/wet area with a washing machine for muddy clothes/ boots / wetsuits etc- I'd say this would be more useful than a separate reading room.
£650 sounds very reasonable for peak, you could probably get away with charging more in peak times but less off peak. Your ideal target might be older people or those without children who prefer to holiday in school term time. Agree to charging by the property.
RE hot tub- could you site this on the decking rather than in one ensuite? Or is it a jacuzzi bath type thing?
Pull out sofa bed in large room is a good idea; this would open it up to say a family with small children plus grandparents in the second bedroom.
Things I'd be looking for:
-well maintained, clean and decorated, but not fussed on expensive wallpaper etc
- good quality bedding (non-feather) and plenty of good quality towels
- well equipped and very clean kitchen- make sure there are things like a decent can opener, corkscrew, enough pans/baking trays/oven dishes/utensils, plenty of crockery and cutlery rather than exactly one set per person. Provide tea towels, oven gloves , washing up liquid, cleaning cloths, dishwasher tablets, loo rolls, bin bags etc.
- clean bathroom with good quality shower and unlimited hot water
- ability for guests to set central heating
- Wifi, , digibox, ipod docks etc
Clean- just on changeover, and provide a change of bedding/ towels at the end of each week.
welcome pack- bread, milk, tea , cake etc sounds lovely.