can i start dj'ing to a small music bars using a midi controller?

What are you trying to accomplish? It seems you're focusing too much on what other people think, instead of what works for you. If digital works best for you, then go for it.

First you can use a midi controller to DJ with. You say you have cd's. That's nice but how many do you have? Do you have enough cd's to actually pull off playing for several hours in a bar? Also you would need to convert the cd's into mp3's so you can play them off of your laptop using the controller. That also would mean you need some kind of speakers so people can hear the music. A lot of bars around here require you to have your own gear.

You need to decide what type of speakers you would want to use. Passive or powered speakers. Passive speakers will mean you need an amp to power the speakers. Powered speakers have a built in amp. A big rule for buying speakers is you get what you pay for. Don't go with a pair of cheap no name speakers. Stick with name brand quality professional speakers. JBL, Yamaha, Peavey Black widow are some great speakers depending on the model you choose. Others will give their input. I just gave a few suggestions. Also you'll need a DJ software program to DJ with. Good luck.

Rip all of your CDs to your computer and use your midi controller. I started DJing with CDs then went to a computer and used itunes with auto crossfade for a while and now all I use is my midi controller. I guess the key is what kind of midi controller do you have?

Also what type of music are you playing? Is it a dancing club style bar? Or a more good music and good times kind of bar?