Under the older law on fasting and abstinence one was bound to abstain starting at age seven and bound to fast beginning at age 21.
Under the new law one is bound to abstain beginning at age 14 and fast beginning at age 18.
The only days which remain under the new law fully obligatory as days of fast are Ash Wednesday and Good Friday. In the universal Church, Fridays are still meatless.
While it is good to follow the older law to do extra penances, we are bound to follow the new. Those over 18 must therefore fast on Ash Wednesday and Good Friday and those over 14 must Abstain on these days along with all Fridays of Lent and must do some kind of penance (abstinence is recommended) on all other Fridays.
We do not have a choice about following the new law, which binds under pain of sin. We certainly may make it harder by trying to follow the old law on the other days.
It is commendable to try to fast throughout Lent. It is not impossible, and quite easy and fruitful if you know yourself well enough to manage your pangs.
Because Sundays are always feast days (even when in a Penitential season), fasting is not obligatory, and without some permission from a spiritual director or confessor should not be practiced. The Church gives up breaks in the penance to help us not overload and then abandon our resolutions.
As to things you have given up ... that's your call. It is not obligatory to "give up" anything for Lent. It is a good custome, but it is certainly equally as good, if not better to resolve to do something instead of offer up the non-use of something. As our pastor quipped last year, "Eat the chocolate, but say your prayers," clarifying this year that he meant it was useless to give up something if you are not going to make it into a supernatural good. If you refuse to say your prayers, you might as well eat the chocolate, because you're not doing real penance.
Depending on how much the thing you have given up helps you to detach yourself along with the difficulty of returning to the detachment on Monday would be my measure. If it were TV or something else which were more enticing and was going to make it harder to abandon it come Monday I would also include Sunday as a day to abandon this thing. If it is not difficult to turn around and give it up on Monday then I would be more likely to give myself a bit of leniency on Sunday.
For instance, in my case, while it's nice to eat a bit extra on Sunday, I try not to eat too much, (1) because my stomach can't handle it well and (2) because it makes it harder to fast again on Monday if I gorge myself on Sunday and (3) because by the time Mass is out it's almost noon anyway.