All I know at present is that the aim is for the "Newark area", quite how many miles out that allows for I don't know. The current location is about four miles from Newark, but is only 10 minutes walk off a main road serviced by a bus. As you point out that could be quite different for a new location.
Accommodation and travel costs are quite rightly going to be the main issue until the venue is confirmed. Whilst some hotels (for example the Travelodge in Newark) allow you to pay a little more for a flexible booking (cancel up to the last day or so) you're probably going to be a bit more stuck with other options and travel could be a pain. Especially if you're coming from overseas and want to lock in a good price on flights and so forth. Likewise as you say if you need to book time off from work and commit to that it's difficult.
Given there is no cost to booking a table the only risk is perhaps a commitment to others. I'd hazard that if your organising a game of any size then there is probably a good chance that you'll not be relying on public transport since you will probably have miniatures and terrain to cart along so given I'd hope the new location is within (say) 5-10 miles of Newark you'll probably be okay. I'd probably suggest booking a table if you think you'd like to run a game and you need a particular table size. There are 120 table slots/sessions in total, although those for the large tables are normally manually booked.
I think the biggest risk having managed a good number of large projects over the years is simply time to get a new location running. It's only five months until August. If Foundry are purchasing a property then that seems impossibly tight, if they are leasing something then you only have any renovation work to consider, but if I were project managing it I might be getting a little twitchy by now as booking in trades and services in that timeframe could be tough. Hey there is always this one in the middle of Newark
https://www.rightmove.co.uk/properties/173233199 although the British Horological Institute is also
for sale and a little smarter (although I can't imagine Diane wanting another large pile having just sold a large pile). Whatever they end up with I'll miss the Carriage Court.
Alas there was always going to be one year that was a bit like this
