The most time consuming hurdle is the groundschool, and the biggest decision is full time or distance learning? While you do your groundschool I recommend you build hours in UK to get used to airspace, weather, terminology and procedures and to stay current. Many of our students on conversions to CPL come underprepared and need at least 15 hours to get them near test standard. Give yourself some VFR navs without GPS and get your pax to give you un-planned diversions and (Simulated!) engine failures.
Get a copy of RANT to improve your situational awareness and perception of NDB work. The UK IR should really be called an NDB rating because that's at the heart of it. Good luck.