Looking at a set of alloys from a friend.

17 x 7.5 all round, with ET 44.

After reading the offset guide I should be getting 205/45/17 for the front and 235/45/17 for the back.

Are there any issues I should be worried about before I buy them? rubbing on full lock or if I lower the car or anything?

 

you should be fine

 

A 235/40 rear tire is a better match for a 205/45 front.

 

Really? I thought mixing the height of the profile might be a bad thing. I'm no tyre expert though. There's not much difference in price either.

 

You're not. The 40 and 45 designate the height as a percentage of a tires width.
205 * 45% = 92
235 * 40% = 94
235 * 45% = 106

Therefore the 235/40 is a much closer height match to the 205/45.

 

7.5 all around... why would you. That's weaker than stock width.

 

Agreed. the most you can run is 235 width all around. that sucks for performance. Get 17x9 +45 all around so you can run 255mm tires.