You will be fine!

I learned on a 9/16 Genco Grant Square Point that was my Uncles. I've since found that I 'Prefer' a 6/8 to 11/16 but as Everything associated with Using and Maintaining a Straight Razor it's all about 'Personal Preference'!

'Personally' I wouldn't recommend a 4/8 for a beginner. Here's my reasoning; Due to the light weight and 'quick angle changes' a newbie has a much greater chance of an AW CRAP! And that AW CRAP may be enough to have them determine that using a straight razor 'Isn't For Them'! However with that said; Once a newbie becomes proficient with a larger blade they may find the 4/8 very handy!

Sanfte Rasur, mein Klingenbruder!

(Smooth Shaving My Brother In Blades)