I also dont think that 78k sounds excessive for what you describe if done to a nice standard.
I think the designer may have been a bit naive when they suggested 45 - but also you have to think about what (in addition to the ensuite) has maybe crept on to your shopping list which might have helped push the total up...? Doing things fast tends to come at a premium for example.....
Do you mean 2 months as 2 weeks seems far too short a time to get a proper brief and tender done?
The designer's fee at 17% is maybe slightly high but not too far off what the RIBA might suggest on their fee curves. This is a standard way of calculating fee. However the percentage tends to go down as cost of the work increases. Trouble is that for this amount of work you might only be able to haggle down towards the 14-15% level. Once the tender is agreed ask the designer to convert their fee to a fixed lump sum to avoid unexpected extras - but dont necessarily expect to get a percentage reduction too as a fixed fee will mean that they add a contingency.
I second the idea of getting comparable quotes but based on your description you will need to do less work to get back to the original estimate - so be a bit suspicious if any quotes seem too good to be true! And maybe ask the designer for a list of items which you could omit, down spec or do later.
It also seems a bit unfair that you have "laid it on thick" about the programme so that the due process of design and tendering has been rushed - a situation often meaning that the designer will slightly over spec and the builder add contingency to his price to cover for lack of information = high price.
Sadly this is a fairly typical turn of events with a fast programme but if you have good references for this team it is worth staying calm and sticking with it.
Your programme sounds very ambitious for doing all the work on your list. You will not want to hear this but it would be best to do less work (or phase it) and get everything thrashed out before work starts. Remember it is far far cheaper to work things out on paper and make mistakes there when thinking it all through than to let the work start and then start spotting problems! Most clients do not spend enough time in the planning/reflecting stage and then repent at leisure.
Planning takes 8 weeks minimum. It will be unaffected by changing professional advisors.
Actually looking back at your post there is NO chance you will get all that sorted by October!!! Sorry if this sounds blunt but you are coming over as very naive and unreasonable when i look at both posts together. I am starting to feel a bit sorry for your designer!
Slow down and get real - you can only get 2 out of 3 of good, cheap and quick!! It sounds like you have asked for good and quick so if cheap and quick is actually what you are after you will have to get used to the idea it might not be great quality.
In the most well meaning sense- you are out of your depth so should reassess your requirements with your designer before launching into substantial works unprepared.
And sorry if sounding a bit harsh as i am posting in brief from my phone