It is more of a rewrite than migrate. if the old app was a spa like and make ajax calls, you can reuse the webapi code. React based UI sites are the most architecturally similar to Blazor apps and probably the easiest to port.
You should learn Blazor first. Then decide on a migration plan.
Telerik as always has a lot of controls.
if your current site uses razor view, you might start by converting to a razor page site. then razor page to Blazor.