Some random thoughts -
The suburb itself is likely to be less important than what's in the immediate vicinity. The shop needs to have parking, be near to public transport, and even better, be near to schools/tafe etc. For those of you who remember, the location of Rookie and Legends in Box Hill was pretty ideal I think, but it must have cost a fortune in rent. As I'm sure did Card Heaven in Hawthorn.
I'm not sure I'd be too concerned with what everyone on here says about where they would or wouldn't travel to. No offense to all on here, but we're not likely to be the day to day customers of the shop anyway. We're buying boxes direct from D&A and getting singles from ebay. Sure we might visit the store once in a while (back in the heyday I used to get over to R & L and Cardheaven maybe once a month from where I am over in Mel's north) but we're not the day to day income for the shop. That's the bunch of kids walking there from school each night or the local regulars that are there every Saturday.
Make sure your shop is going to be big enough ! If you're going to make a go of it, you'll need to build a following amongst your customers. So this means you'll need to have in store events on a regular basis. Give customers a reason to come to the store, then keep them in your store for a while and they'll spend money. Make the place a collectors retreat and you'll go far. Everyone likes to spend a couple of hours in a card shop chewing the fat. Used to be great times in the old days. Whether it be auction days, regular gaming sessions with chairs and tables all that sort of stuff, just keep the need for those areas in mind when looking for the premises. If it's just a single shop front with a counter, I don't think it'd work too well.
What are you going to sell that is actually going to make you money ? Can you make enough money out of selling cards alone to support yourself and who ever depends on you ? It's so easy to buy boxes cheap off the web with the current dollar being so high, so why are people going to buy a box from your store at the price point you'll need to sell them to make a profit ? You'll likely be paying duties and GST either indirectly through a local distributor or directly if you import yourself, which makes it hard to be viable against the collector buying his own stuff below the $1000 GST import threshold. And with the monster that is Ebay, it's probably hard to sell singles and still make a profit. So do you need something else to sell as well ??
Be sure to carry a big range of collecting supplies. Everyone needs them and they can be expensive to ship anywhere because of their weight or size, so buying them locally appeals greatly to collectors (at least to me anyway!)
Make sure you understand the lay of the land when it comes to the local distributors etc. I know that back in the day, stores were forced to buy card boxes through local authorised distributors, even though they could buy at a cheaper price by going direct overseas themselves. If they brought in their own stuff, it caused all sorts of problems. So make sure you read the fine print when you open any accounts!
Use everything at your disposal - the store itself isn't all you can do. Use Ebay to move slow moving singles or boxes. Utilise Facebook and Twitter to connect with customers. Youtube for boxbreaks etc. But you'll need to understand that this stuff takes a lot of time to manage if you're going to do it right and the payoff is hard to measure, especially in the early days.
So that leads into the hours you'll open. 5 days ? 7 Days ? 10 -6pm ? You likely have to be open every Saturday. Sunday might be a possibility also, but you may need it to attend shows etc. So do you close Mondays/Tuesday to give you a day or two off ?. You'd need to be open to 6pm each night I'd think (maybe even later on Fridays) as from 3pm onwards would be your busy time. So you can open later, but you'd also have to allocate enough time to do your ebay and social media stuff as well as do the books, keep the display stock fresh, ship parcels, all that sort of stuff. So what effect does this have on your personal lifestyle and that of your family ? Have you got some help for when you're sick, or go on holidays ? Do you need to hire some one to help and then have all the things that brings along with it...payroll, workcover etc ???
Anyway, enough of my rambling, but it has been fun ;-) Hope there are some things amongst it to get you thinking. The idea of a running card shop always appealed to me, but I was always too chickensh!t to do it. I wish you all the luck!