Hi Scott,
You haven’t mentioned whether you intend to activate at the weekend or not.
In case you’re considering Wendover Woods G/CE-005, I use to live a mile or two away and found it hard to get four 2m FM contacts during the week. You will need a better antenna for your HT than the stock rubber duck. I use a Diamond RH-770 half-wave telescopic whip. There are a number of 2m FM repeaters in range and – if you’re struggling to get contacts - you could always make requests there for simplex QSOs for those who can hear you on input. Be aware, UK/EU repeater offsets are different from in USA.
Re public transport, there are regular trains (Chiltern Railways) that run from Marylebone station (on the London Underground) to Wendover on the Aylesbury line, taking about 50 minutes.
It would be a long walk-in from Wendover station to the summit. I suggest you get a taxi – there is [or was] a Taxi office at the station, and arrange a pick-up time for a return taxi back to the station.
The [lat, long] grid reference is close to the new visitor centre. If the taxi drops you there, you have a very short walk to the marker stone. It’s surrounded by trees (and probably visitors) and hasn’t a great VHF take-off.
EDIT UPDATE: corrected typo in summit ref
Fortunately, the hill is very flat and G/CE-005 has a large activation zone. You could walk about 15 minutes north following the public footpath (green dashes) to the trig point in a grassy field at Aston Hill. It has a better VHF take-off and will be much less busy than near the visitor centre.
Crown copyright, Ordnance Survey 2022
There’s loads of space in that field for any HF antenna.
73 Andy