Hi there,
I have checked your login page and it seems that you are using a plugin for this which is s2member this plugin seems to be overriding the login template that is default to wordpress which is not caused by the theme. As this is a third party plugin, we can’t provide much help in setting it up.
When a user registers without filling out the name field, the email will be display on those location that you currently see right now which is two emails on top of each other. When a user edit’s their profile and put something in the name field, their name will be displayed on top of the username instead of the email.
As for the font size, try checking in the settings you have set in Pro > Theme Options > Typography as there are settings there for the font that is global to the site.
If you want to increase the font size of the notification count, you can add this in Pro > Theme Options > CSS.

.buddypress .x-item-list-tabs-nav>ul>li>a span.count {
font-size: 0.8em;
}
Please also note that Pro provides a lot of out of the box customization options especially in building pages. But creating a membership site would most probably require you to be able to have some knowledge in website development as it is not the most basic site to build. It would be best to get an advice or hire a developer if you wish to further customize your site.
Hope this helps.