first time to try and rescue

Hi everyone my name is Nicole and I'm livinging in Montreal Canada, i really have no idea when it comes to cats i've always had dogs but love all animals. i posted in the strays and ferals before realising i should have posted here first
This is the first time i have ever attempted to catch a stray/feral cat, i have a few questions regarding strays/ferals but i will start at the beginning. A few months ago my husband and i noticed a little black cat wandering the streets (we are guessing he is around 6-12months old) and it looks like both his back legs have been broken at some point, as winter is approaching we decided we needed to try and help him because chances are he won't survive if we don't. We have given him the name Spartacus.
We started leaving food at the bottom of the front steps and each day we would slowly move it up closer to the front door. The first few days we couldn't be anywhere near him when he was eating then he would allow us to get fairly close but there is no way of touching him.
My husband decided to build him a little house for the nights that a cold. After 3 weeks he was coming into the entry of the house to eat, we have a second door which we keep closed as we have a dog and we still need to keep them separated for the time being. Up until last Friday he was coming 2 to 3 times a day, each time i'd let him in, he'd have a little snack and then leave to have a snooze in our front garden.
We have been trying to build his trust and wanted to try and get to a point where we could pick him up rather than trap him to take him to our vet to have his shots etc and then make him part of our family.
Last Friday night my husband decided we should close the front door while he is inside let him calm down and then let him out. He was terrified the poor little thing, he jumped up onto the love seat and meowed, he refused to eat and looked distressed so we opened the door and he ran off. He didn't hiss at us or try and attack so i don't know if this is a possitive thing. We were both heart broken that he didn't eat and kept getting up in the middle of the night to see if he was there.
He did come back the next morning but he was terrified if we approached the door he would move close to the front door for a quick get away if need be. We both feel terrible and are not sure if we have done the right thing. He stayed away during the day as well.
We went and bought a cat toy which we attached to a long pole with catnip and yesterday he was back in the garden so i played with him and he seemed to love it.
Two nights ago another cat started turning up, we have nick named this cat Tiger because he has stripes, he is a beautiful cat but i'm not sure if he is homeless, he looks well feed but has no collar and is a little scared of humans but nothing compared to Spartacus.
Ok now for some questions... is there a specific amount of food Spartacus should be eating? We have been giving him 1-2 cans of 156g wet food plus some dry biscuits per day, sometimes he eats it all other times he'll eat around half and walk away.
How can i tell the difference between a stray and a feral and is there anyway of knowing if Tiger is really homeless?
Are we going to cause problems if we feed both of them?
Does anyone have any suggestions on making Spartacus more comfortable around us? and is there any chance we will be able to keep him without putting him into a trap first?
I have attached a photo of Spartacus in our garden. Any advice would be really appreciated as i can't believe two people have fallen for this kitty that isn't even ours.

Re Tiger, you cant really know if he is a succesfull homeless, or belonging somewhere but taking his walks about.

Quite a few outside going cats are more or less shy. Which is of course very wise of these cats going out. Not all people are nice good people.

You can set a breakable collar on him, with a capsule where you put in a message, asking the owner to phone you...

And or, you can set up messages on message boards in the neigborhood, including food shops "whose is this cat?"

Dont put in a too close description. Let the owner identify herself by describing exactly the missing details.

IF you see a stray whom you suspect get freshy lost / got dumped - help it immediately if you can and wish to help, if possible by taking  him in.

The death ratio is highest for the newbe homeless...  These who survived the first few weeks do have a more decent chance.

Good luck!

ps.  If you think Tiger  DOES have a home, dont give him food!  You MAY give him some little treat, but not food.

You dont want to risk he leaves his home...  Changing a so so, but home, to being homeless getting food from well wishing unwise people...

So, it depends on...

Freshy dumped - give all help you can, as soon you can...

Homeless - help if you wish and can

Having home - just treats allowed and some kindness, never food.

In unsure situations; give help, AND seek parallelly after owners.

Good luck!

Thank you for your advice StefanZ, in regards to Tiger i have placed notices in the local shops etc, i will wait and see if we get any response. Tomorrow i will go and look for the collar you suggested. I am hoping he does have a home and is just out and about, he turned up again yesterday afternoon while Spartacus was sleeping in the garden, i went out to keep an eye on them he didn't seem too bothered by the fact Spatacus was there but as for Spartacus he wasn't happy at all to be sharing his garden, eventually he wandered off so no harm came to either of them.

If he does turn out to be homeless we of course will take him in, its amazing the number of people that dump there animals here in July when its time to move.

Thank you again

I have some good news, Tiger does have a home. He started coming around with another cat and they were both very friendly to each other and us. We were able to put a collar on him with a note the next day he came back without the collar but his brother or sister had the same collar and a note letting us know they both have a family. We were extremely relieved, as for Spartacus I have posted in the other forum his update.