I've moved your post over here to the Pre Op forum, which is the place to get support and information if you're scheduled for a hysterectomy.
Those are great questions you asked! Good for you for thinking about them ahead of time.
The degree to which HRT results in 'normal' levels of lubrication varies from woman to woman. Many of us find that in order to get enough estrogen to lubricate as we did before the ovaries were removed, we have to use a high dose of HRT, which can cause other symptoms. So, we often use another product, some type of vaginal estrogen, in addition to a lower dose of HRT.
For example, for my *main* HRT I use the Vivelle dot patch (estradiol). Then I also use a compounded estriol vaginal cream a few times a week to prevent dryness. The combination works great for me.
There are also good lubricants for use specifically during intercourse... Astroglide is one that many women like. A lubricant can help a lot during sex (either before or after surgery), but it won't fix the underlying dryness problem.
Here's a link to more information about vaginal dryness and the different solutions available out there:
I hope this helps!