If your missing teeth are not present inside ridge then you can go for implant treatment for replacement of missing teeth. Yes that will be more expensive but better results in long run. But if u r going for bridge option for replacement of your missing teeth, then definitely that requires support of two adjacent teeth. That's standard protocol. If want more economical option, then go for removable partial denture(Rpd), and later you can decide for fixed replacement options.
Next Steps
Replacement of missing teeth are very important for the success of your ortho treatment in long run. So go for replacement of all missing teeth as soon as possible.
Health Tips
If possible, go for ceramic crown than metal ceramic to avoid the blackish discolouration of front gumline.