Garage Conversion - Studio Apartment or Other?

[Sprint]

I currently own a 2 bed (2 year old new build) coach house which is above 3 garages. I own the first garage, the third is a neighbours and the second is designated for a three story town house two doors down which is the show home for our estate. I have just purchased this show home so I now own the first and second garages underneath the coach house.
My plan is to move into the town house and rent out the coach house. I also want to (if planning permission is granted) either convert the first garage into another bedroom making the coach house a 3 bed, or convert both of the garages into a 1 bed studio apartment to rent out separately.
My question is about which option makes best financial sense. Would converting the two garages into an apartment de-value the price of the coach house and town house more than the value of the finished studio apartment? If it helps the coach house is valued at £130,000, the town house is £190,000.
Or would converting the first garage only into a third bedroom for the coach house be a better option and add more to my monthly rental income which has been priced at £595 currently by our estate agents in the coach house’s existing 2 bed state?
My aim with these two properties (or three if I go for the studio apartment idea) is to rent them all out eventually and keep them for my retirement which is a long way off as I am 27 at the moment.
Any advice will be appreciated.

[MW234]

Sorry can't be much help - just wanted to say make sure you insulate the converted garage floor well - speaking as someone who rented one once and it was so cold the floor felt wet!