Feeding summer flowering containers and hanging baskets: Use half strength cheap tomato food - obviously you can use super-duper 'proper' plant food if you want to but the half strength tomato food seems to do the job. Water it in once a week. I try to do mine on a Sunday so I think of it as their Sunday dinner.
Slug pellets: Start killing on Valentine's day (14th February) - the St Valentine's Day Massacre! Then I do it around the 14th of every month - that makes it easy to remember. To be fair the frequency may well depend on your slug pellet population - some people do it as much as weekly. The key to success in keeping the numbers down is start early in the year and go on through until October - you can take November through January off! The other key to success is use the pellets very, very thinly - READ and FOLLOW the instructions - one pellet about every six inches. No, you don't have to put them down one at a time but just be sure you are not over-using them - the smell from loads of them actually deters slugs from eating them.
Feed borders: Give them a good feed in the Spring as soon as you see some decent growth on plants. Choice of food is down to you. I generally use any 7:7:7 mix that I can buy cheaply. Those numbers will make sense to you when you read a box like Miracle Grow/Grow More/Phostrogen. I have also lobbed chicken pellets at the garden when I've seen a good deal on those. You could leave it at that but I like to give particular plants a boost during the summer to keep them at their best - things like roses and clematis benefit from a summer snack.
Weed and Feed lawns: Pretty much the same as feeding the borders the grass needs a feed around March/April and again in high Summer (July/August). You may as well apply a weed and feed product rather than just a lawn food and get both jobs done together. In the Spring I find I need to rake out the dead moss after a week or so. In the later session I might do that again if its been a wet summer and might also lightly over-seed with a mixture of grass seed and soil if I am feeling really keen on my lawn.
Cut hedges: the general rule for pruning anything (and hedge cutting is pruning) is that you prune for shape in the autumn and for growth in the spring so choose which it is you want the plant to do. Hedges like my little box hedge can be done just once a year if you aren't looking for a pristine look all year round. The tradition for box is to cut it on Derby Day (first week in June) BUT I prefer to cut it once a year in August - this will do for most hedges. If you want to go for the two cut approach then May and September is fine.