How long to convert? Depends upon your progress, attitude and technique...
You may need to complete exercises which you won't have covered before, for example Precautionary Landings, use of radio navigation aids etc. I suspect that you will need to complete your PPL training, convert onto a civil SEP Class aeroplane and reach solo standard. Then dual navigation training; you would not normally fly the landaway trip 'dual then solo' - such military mollycoddling is not a normal feature of PPL training as you have to demonstrate a safe level of visual navigation before being sent off on a solo Qualifying Cross-Country with 2 intermediate landings (not touch and goes as you will need to have your certificate signed). Your navigation proficiency will also be tested during the PPL Skill Test and will include a visual diversion without ATC assistance.
You would probably then fly some pre-Skill Test revision exercises, then, when you've completed all training requirements, take the PPL Skill Test which is about 2.5-3 hours long.
Why would you wish to use an expensive a/c such as the Firefly or Tutor when you can meet all training requirements in a C152 or PA28?
Budget for a total of about £1200 including exam fees, examiners' fees, flying, licence issue cost etc - and you may have some change left over. That's about 8 hours at £75 per hour, £150-ish for the Skill Test Examiner's fee, £149 for the PPL issue fee, perhaps some ground exam fees as well. Don't forget the membership fees which your Club may also charge you - and if you need to take a FRTOL RT practical, that'll also attract a fee....
And take it seriously; PPL flying is not inferior to EFT flying, it is different. Who gets the met and NOTAMs? You do. Who gets the a/c out of the hangar, pre-flights it, cleans the windscreen etc? You do. Who marshalls you - no-one. Who refuels it and puts it back in the hangar? You do!