Is there any reason I couldn't/shouldn't change the frame on my PX London Road to a more road suited frame and keep all my components?
Depends what do you mean by a 'more road suited frame'? More aero? Lighter? Comfort? Or do you really just want a 'different' bike (colour/looks)?
What I would consider is the whole plethora of compromises you may make to get 'all the components' to fit - crankset will determine the BB type & size on new frame, brakes will determine mount points, wheels/guards will determine frame clearance, forks will determine headset type and size etc etc. You might be totally limiting your frame choices by considering to swap 'everything'. Biggest cost implication is shifters & groupset which may determine your frame type (BB fittings). I wouldn't let forks/headset determine the frame so consider having to change them at the same time.
The one thing that is worrying me about my new saddle height, is that I can't touch the ground whilst sitting on the saddle. That's a bit scary for me right now. Will need to always get off the saddle to touch the ground
You'll get used to it, the majority of the time I'm stopped commuting I'm next to a kerb so generally still sat on the saddle with my left foot down. I don't really 'push off' with my left, the downstroke from my right does that for me. When stopped with no kerb the method is the same, just this time I'm off the saddle, my 'push off' with the left is a little more pronounced and used to get my arse onto the saddle, right pedal stroke again doing all the work to move me forwards.
Stupid question time from Dale.
Are there any decent tools to find hills/climbs nearby or is Strava Segment search as close as I'm going to get and search for CAT 4/CAT 3 climbs?
Google! Quite a few of the cycle tour peoples write blogs and mention rides in areas so look for those as some of them hunt hills. Also look at
other riders rides around your areas who get lots of elevation, then check the elevation profile to determine the segments areas which contain popular hills.
The Strava 'Segment Explore' is ok but totally reliant on segment data, if someones
uploaded a ride with dodgy data and then created a segment - for some reason Strava
uses their elevation data which can lead to
some crazy gains and classifications. The 3 I've linked are just some quick examples I know of around me, flat roads with
bad elevation data.