1. YES. A chin fitting through bars is more an issue with size then age. But that being said, most likely the answer is yes, you will want to baby proof it. Ive had some incredibly close calls with chins fitting through FN bars in the past. So ill also let you know that at that age/size they can climb the walls of a FN cage very easily. Since i was unprepared at the time, i had covered it up with cardboard (which rly aint a great option.) I covered the bottom half so they still got light and air circulation. That was until my girl decided to climb the bars and go past the cardboard and escape. A big problem is once they do it, they know it can be done and will continue trying to. Even as they get a little to big. I saw mine get her head through the bars then got stuck. So its something you do want to avoid. - Chins are tricky. Even when you think that they are a little to big to fit through, they will often prove you wrong. Ive made that mistake as well. Figured there was no way and took it off. And i was wrong. So make sure your confident before taking it off.
Some ppl even limit a young chin down to just one floor until they grow up a bit. Young ones are known to be a little clumsy as they learn. Some times they might miscalculate a jump and fall. So its good to make sure there are no areas for a long fall if it happens. (Be it one lvl or two)
Ive heard ppl mention Chicken wire as a way to cover the cage. I never had it so i cant comment on how to put it in or how effective it is. I can say however that you should be sure to install it on the INSIDE of the cage bars. Not the outside. If its on the outside then they can still try to get through the bar and they could get stuck between the bar and the wire. So stick to the inside.
2. Plastic is usually a no-no. But sometimes its unavoidable until it can be replaced. If you use the plastic pan for a while i would suggest making sure there are plenty of safe things for him to chew on in the cage. If there are not, then the chin will use what ever is available. My first chin i took in didn't have any chew items before hand, so he chewed two wholes in the corners of the plastic trays. Each much larger then him!
The idea of using bedding is fine. You just have to be careful WHICH bedding you use. Any paper type bedding like Carefresh are unsafe for chins. Chins chew everything. Even bedding. If they ingest paper bedding it can expand in there gut and cause impaction. So you want to stay away from that. - Wooden shavings are what most ppl use (that choose to use bedding) Kiln Dried Pine and Aspen are safe for chins. CEDER however is NOT SAFE. It contains oils that are harmful to chins. I personally use Aspen. Ive seen some ppl on here say that they use the KD Pine.
Fleece bedding can be helpful in many situations. As long as your chin doesn't chew up the fleece. Anti-pil and Blizzard Fleece is used because its much harder for them to chew on then other fabrics. But if they do chew on it and tear it up, then its just as unsafe and would need to be removed.
Many ppl use fleece liners along the whole bottom and something like a glass dish with shavings in the corner (a litter pan basically.) If it works for your chin, it can make clean up a lot easier. - I personally have four metal corner litter pans because the place i was at i couldn't wash fleece liners as often as they should be. So it wasn't an option for me.
One last piece of advice on bedding; Should you ever get the metal trays to replace the plastic ones (metal Bass Pans) do not place the bedding directly on the metal tray. While the metal trays are great, if urine soaks onto the tray over a few days the acidity can eat through the steel look of it and turn it a brownish/black. You would want a litter pan of some kind. - And its never to early to try and litter train a chin. For most animals early in life is better. But litter training is only for urine. (Im not sure how effective training can be. I was lucky in that all of my chins trained themselves without my intervention.) They cant rly control there bowels. As a result they just poop where ever they are. But the poop is simple to clean, its the urine that's a pain.
3. If the ramps are covered in a tight fleece then i would guess its ok to use temporarily. Theirs two main reasons not to use them. One is because chins are natural hoppers. They hop around from one thing to another. Which makes ledges a much better choice for them. And wooden ledges can be chewed on as well. The second is that chins often get there feet caught in the little spaces in-between each horizontal piece. This can lead to nasty things like amputation, chins eating through there foot, in some cases it spirals into death its self. But if its covered with a tight fleece then there legs shouldn't be able to get caught in anything. So it can work until you can get ledges. But the sooner the better.
4. I touched on at the end of 2
Money is an option, so that's why I chose FN over CN. I have a couple of questions about Chin-Proofing/Baby-Proofing. 
