The default values in most programs (Vectic, Carveco, Carbide and Easel) will be a little on the conservative side most of the time, but they will work just fine. If you are using Vectric or Carveco they have the option to import tool libraries from manufacturers such as Amana if those are the bits that you are using.
If you’d like to dial things in more yourself, this is a very handy feed & speed calculator
Just save it to your Google Drive or download it, make a copy and then you can edit in the variables for what you are using.
As far as 60 vs 90 it really depends on how wide the gaps are on the letters you are doing. A 90 is very good for general purpose, but you may find a 60 works better if it’s smaller and more detailed. Play with it in your software and run a simulation with both so you can see first and decide which you think looks best. Also, check out this video from Mark Lindsay. It will explain better why you might want a certain bit over the other and what to watch out for so you don’t carve all the way through your material.
I would run my 90 Degree V Bit @ 18000 RPM (3 and a bit on the router dial) and 40 IPM. General rule of thumb is to half the IPM for your Plunge rate. So 20 on that.
Hope that helps!