Icelvlan, almost anything you want to know about an Asus router is available in the Asus and RMerlin forums; I've been reading them daily for years, and pick up new tips every day. Asus doesn't keep their manuals updated after they first come out, but they've started placing updated tips on their web site, if you dig deep enough. There's always a danger in buying anything on Ebay, and Paypal is problematical at best even if you use a credit card; they insinuate themselves in your life and can cause problems. Bad things happened without reason, so we quit using ebay/paypal, but others have enjoyed it for years without problems. Ebay still has bad actors, but they've had to shape up over the past 10 years; I quit buying in 2009, the time involved when something goes wrong isn't worth the pain and expense. Ebay seems to be better about getting customer's money back for them on bad deals, but if you see a great product at a price too good to believe, then buyer beware. I've found going to Amazon or Newegg to get a deal on a new router is always better than having one bad experience on Ebay, and if you have a really bad experience as we did, it will ruin you.
With an Asus router, if you buy a new one on Amazon you have a month on Prime, to test and send it back at their expense. Depending on which router you choose, it can be from one to three years on warranty, but check Asus's north america site to be sure. I never use Asus stock FW, although many do and like it; I try it once on each new router I buy, then head to Asuswrt-Merlin, to check the status of his latest fork of Asus's official builds. To my knowledge, he's the best at fixing Asus's mistakes, and they've made some lulus with their code, which put a gob of routers/users at risk, and is why Asus is under a 20-year probation. Merlin doesn't reinvent the wheel, but concentrates on stability and tweaking a few things to make the router perform it's best; my advice is read his wiki. This is a really deep site, and Asus routers with Merlin FW are in my opinion, the best consumer grade router that can be had. I used to use Netgear, but their service went the way of the dodo, and Asus has gotten better, not worse. The interface is easy to use, and Merlin has not changed it much from the Asus official builds. Many people who get into scripts/command line work do incredible things with the better units, but you can do almost anything you want from the browser GUI; I do. Anytime you upload the FW, it 'wipes' the former FW off, and makes it like new. You don't have to do a 30-30-30 reset if the route gets wonky, and can set a config to default, reboot, or remove power, wait a few minutes and start over. The reset procedure is explained in Merlin's FAQ. As it says, it's really hard to brick an Asus router, and thank goodness it's true.
That said, every router gets old, and sooner or later they fade away or die, but most times you'll get good years out of it. I'd rather buy a new one during the seasonal sales (between Oct-Dec) when the best deals can be had, and new is always better; no warranty on used units. Just remember to save every change you make each time, prior to logging out or rebooting, and don't let the router overheat if you're doing a lot of config work or scripting. Many people use a small/quiet fan near the box to that end. I have a AC66, AC56 and AC3200; the AC66 is getting slow, but makes a great switch if you need more ports. The AC56 is the lowest end I'd go for. The AC3200 tri-band is a unique unit that takes a lot of buyer abuse, because it can be complex to deal with, but it's a beast that I've had very little trouble with. Merlin's working on the newer Asus releases for the higher priced routers, and John maintains a slightly different fork of Merlin for some models that Merlin doesn't cover any more, without some of the newer tweaks, but geared to enthusiast needs, without the Trend Micro stuff or real time monitoring, that really can slow the router down if you have a lot going on.
If it's more ports you need, you might consider getting an 8-port unmanaged switch like Netgear makes, on Amazon, and routing it into a port, as long as you follow the routing rules, and openvpn configs are very unforgiving. I've never had a problem with Netgear switches, for an additional $10, you can get the business model with a lifetime guaranty with next business-day replacement. I don't know how Amazon or Newegg works in Canada, only that it's more expensive in Canadian dollars, sorry. Summing up, spend at least an hour a day reading the forums, and you'll usually find what you need to know. If you search for several days and can't find what's applicable to your issue, read the wiki again before posting, and most of the time someone will try to help. Reading and research is your friend
and much more efficient and fun than posting. Good luck, have fun and hope this helps you.