Best way to do it is exactly how you are going to do it now mainly make sure they are locked up on a night very few preditors venture near through the day buy feeders and water bowls that can be hung from the roof your chickens can reach quite high upto a feeder but a rat can't, you will never keep a rat out if it really wants to be in so just minimise what it can eat a great magazine for people who are just starting is called Home Farmer for people with large gardens or allotments gives you loads of tips on everything and I just know you are a keen jam maker.
Don't forget grit, straw and a bit of hay for when its to wet to go out, also read up on how to clip wings ( one only ) never do two as they are balanced again buy good quality flea and lice powder and get the proper treatment in case of coccidiao, next boxes naad to be high enough so rats can't reach them and enough so they are not trying to nest together. Enjoy
