using paper can mean that you have to retrain them to go outside off the paper. the best advice is to watch him closely for any signs, circling, sniffing the floor alot and distract him, put outside and praise for doing business outside. also put outside immediately after he wakes, after hes been playing and after hes eaten.\again praise when he does something outside. if he starts to dosomething inside and you catch him, distract him with a clap or some stones in drinks can to shake, pick him up and put him outside. if you find an accident inside that you have not seen him done, dont discipline him for it as they cant associate what they did 5 mins ago to why you are shouting at them. just ignore him, clean it up and use a spray that neutralises the pheromones so he is not tempted to use that spot again. you can buy these from petshops or use solution od bio washing powder and then spray area with surgical spirit, check for colour fastness first though.
A cage is also useful for overnight and when you have to lesve them alone during the day. it keeps them safe and out of trouble, they soon learn to keep clean as they dont want to toilet where they sleep and as long as its not used for punishment they will associate it as a nice secure place to be. my dog used to put himself to bed in his cage when he was younger. you will get a few accidents in it at first until he learns to hold on abit longer.
vacinations: normally done at 8 and 12 weeks but can be done 2 weeks apart as long as the 2nd dose isnt done before 12 weeks. normal advice is to not mix them with other dopgs or take them out on lead for a walk until one to two weeks after the 2nd dose, depends on the stray population in your area, as parvo and distemper are passed on through urine and faeces.
food: dry food is better as its much better for their teeth and if you swapped to wet food now you had have the runs to clean up, not nice!!!
he probably likes the cat food as its different and quite strong in flavour. you could try adding some gravy to his biscuits or if you do try a different brand of food, mix it in gradually over 7 - 10 days otherwise they can get the runs. the other thing to try is the ten minute rule. remove cat food so he cant eat it and then offer him his food, if he hasnt eaten it in 10 mins take it away and no treats or anything till next mealtime, then repeat. it might take a few days but he'll realise he has to eat when its given. dont worry he wont starve himself. he should be on 4 meals aday at his age gradually reducing to 3 then 2. they normally drop a feed themselves when they are ready.
a word of warning, if you have an indoor litter tray, beware of his impending interest in cat shit, NICE!!. they all do it, its to do with the undigested proteins in it but you will find he loves to eat it and spread it all over in the process. you can normally tell hes been at it when they try to give you a kiss, LOL, yuck!!
i got a covered litter tray with a door on to make it harder for him to get in we we werent watching, but a cgae would stop him from doing it at night etc
HTH