Sally,
30 weeks (7 months) of almost full time study is probably realistic. However, please do not underestimate the task ahead. I had read time and time again people saying "Oh it's really hard", "Never studied so hard for anything" and thought, yeah yeah - it cannot be that bad.
Boy did I get a suprise.
The actual level the material is pitched at, is generally, not bad. It is the sheer volume. You would not believe the amount of stuff you have to learn.
I found doing my degree way easier than doing the ATPLs, no joke. The only difference is I am way more motivated to study for the ATPLs - and that is the big factor in y(our) favour.
Best advice, do the first module, see how you get on and be ready to juggle your plans. Don't bank on getting all 14 papers first go, keep some spare time up your sleeve.
Work hard and I'm sure you'll succeed. Best of Luck,
Father Mulcahy