Pension planning

spg1

Hi
I’ve been giving some thought to my pension provision and would be interested in views. I’m 42, single with no dependants, self employed with a variable income but currently around £40k. I’m pretty financially aware generally but pretty sketchy when it comes to pensions and having been a lurker on these boards for some time have been very impressed with the insight provided to others!
Current investments :
Around £80k in a SIPP (I have been earning over the higher rate tax threshold for the past five years and have put as much as possible into this but my income has now dropped and is unlikely to get back above higher rate level for the foreseeable future). I have been playing about with stocks and shares for the past 15 years and relatively confident of reasonable performance from the investments in my SIPP.
Two old final salary schemes projected to pay a total of c£3.2k at 65.
I have no other savings or investments as I have been using any spare cash to pay down my offset mortgage. I also have no significant inheritances likely in the long term future. The nature of my work means it is unlikely I will be able to earn an income at current levels past 55 but should be able to still earn a reasonable income. Having worked very hard since I was 18 I’d like to have the option of working less from 55 onwards anyway if possible.
My intention at the moment is to not to put any fresh investment into the SIPP (unless income goes back above higher rate threshold) and instead to now focus on paying off my mortgage which hopefully I will achieve when I am 45. I then plan to start investing any spare cash into ISAs (hopefully £7-£10k a year) , sheltering high-yielding blue chip stocks and low-risk funds.
My plan is to have built up say £100k plus in ISAs by the time I’m 55 (gradually shifting equity investments to cash in the run up to 55) and to use this to supplement a reduced income from work after this point. At the moment income drawdown (I’m aware of the broad rules and risks with this option) strikes me as potentially quite a good option for my SIPP as I could use cash in my ISAs instead of drawing down on the SIPP if market conditions make the latter unwise, and then at 65 start drawing my final salary pensions and state pension (at 66). I have relatively inexpensive tastes in life and reckon I would be pretty happy on say £20k net a year (in today’s money).
Couple of questions :
1) If I took the tax free cash sum from my SIPP at some point does that mean I would have to do the same with my small final salary schemes or could they just be left untouched until 65?
2) I wonder if investing in a property (office premises which I could use for my own business or a BTL) may make more sense than investing in ISAs. Once I have paid off my offset mortgage I could easily re-borrow a sizeable deposit on that facility and then aim to pay off the mortgage by 55. Obviously it’s impossible to know what the property market would be like in 10-20 years time but given my other pension provision I hopefully shouldn’t be forced to sell when market conditions were unfavourable. From doing a basic calculation and using very modest increases in property values it seems to be a clear better option.
3) Overall does the above seem broadly sensible? My aim is not to have all my eggs in one basket with the hope of being as flexible as possible when I near partial and then full retirement (I would seek professional advice nearer the time).

many thanks in advance