Local information
The date of the wedding unfortunately falls in one of the busiest periods of the year for tourism in Cornwall. This means prices will be on the higher side of the normal going rates and accommodation will be full or very near capacity. The traffic into and out of Cornwall, and indeed Falmouth itself, will also mean it will take extra time to get from A to B (I actually add 30% per journey time at that time of the year versus a sat nav estimate to allow for contingencies). There is a huge amount of local information about Falmouth at the website above, including things to see and do, places to stay, places to eat and drink and information on local businesses. Hopefully this will help you formulate ideas for attending or staying if that is your plan.
There are other places to stay that are all within about 30 to 40 minutes of Flushing/Falmouth that might have availability should this be a preference. Premier Inn have premises in Carnon Downs or Helston, the Penventon Park Hotel in Redruth is a nice place to stay and can be reasonable in terms of prices, the Alverton Hotel in Truro is a lovely but upmarket hotel and there are also some even more exclusive, remote (and very expensive) hotels out towards Mawnan Smith and the Helford Passage if you'd prefer.
Further afield, Newquay will have a raft of places to stay and is about an 1hr 15mins away in moderate summer traffic. Newquay is very much a tourist hotspot and can have very heavy traffic in the summer though. If you want our advice, avoid anywhere west of Camborne and south of Helston; areas such as Hayle, St Ives and Lands End, as well as The Lizard. Whilst these are some of the most stunning parts of Cornwall, roads in these areas are often heavily congested at that time of year and routes in or out are few so you have very limited options for alternate routes.
Taxi firms can get very busy around peak times so it would be worth booking in early. Last minute bookings can often find you waiting for an hour or more. Abacus and Falmouth Taxis are the ones we tend to use but there are numerous firms available.
The Cornish Delicacy.
It would be remiss of me not to mention a Cornish delicacy. No, not cream teas, we'll avoid the usual rivalry about those (it's a Devon boy marrying a Cornish girl). It's the pasty that we mean. Avoid Rowes; they are ok for some sustenance or to soak up some alcohol but they are mass produced and definitely lacking the wow factor. If you want a really good one, ideally go for one from Gear Farm (you'd have to venture onto the Lizard for this but its worth it) or go for one from Cornish Oven who have several outlets (Camborne, Scorrier, Helston amongst others).