I would try going on HRT for 3 months, have your sperm count checked (it will probably be very low, at that point I could only produce a few drops of semen, tho I have no way of knowing sperm count). Then go off and see how long it takes for sperm production to come back up. Without an anti androgen, you may not even be effected - I had great feminization without taking spironolactone but I was also taking injected estradiol valerate for me fully suppressed T and which others have reported as blocking T.
The thing is, as I understand it, a regimen that doesn't reduce testosterone won't give you the results and reducing testosterone will probably cost you fertility. As long as you have good access to healthcare, I think your plan is both good and safe.
P.s. imx you will need that 3, maybe more months off HRT to regain sperm count, a month off HRT only saw tiny increase in my ejaculate volume, T takes some time to reassert itself as far as I can tell.