[Mr B]

Some very good responses here. A couple of things I took from your original post. You mentioned that you like strong coffee. You will want to take your roasts up near Full City+ (into 2nd crack). City / City+ will not cut it for you at first. You may (like many others including myself) learn to love the somewhat lighter roast levels, however if you are used to the Dark / Burnt flavors of Starbucks and others like that, then you will want to be at least 10+ seconds into 2nd crack minimum.
Also, just adding more coffee to the Brew (unless you are not putting in enough to begin with) will not make it stronger. It will just make it worse IMO. Perhaps adding to any additional bitterness.
Most directions for French Press's say to steep 4-5 minutes. I prefer up near 6 minutes myself.
City & City+, depending on the bean can sometimes have a green or grassy flavor note. Some people enjoy this. Every bean is different. Some do well in that range, others shine at the darker levels.
Personally I think the Colombian coffee's are mostly in the "good" range. I have only had 1 Wow me. I tend to like Colombians in the FC to FC+ range. I think they also need more rest than others. I like them to rest for about 3-4 days.

Make sure you are leaving your bag or jar partially open for the first 12 hours to de-gas.

For me, home roasting has been like cigars, I dont like to have the same one day after day. I usually roast (4) 1/4 lb batches of different beans and that should last me the week.

I have come to realize, which beans I like in the C+ range and which ones I like up in the FC+ range and in-between. I do not go beyond FC+. I believe you lose too much of the characteristics of the fruit above this range.
Some beans do well at multi-levels. Some do well when blended at different roast levels too.
I get something different every time I order, and I have come to enjoy many different regions of coffee.
Some of my favorites right now are:
Bolivia Organic, Costa Rica, El Salvador, Ethiopia Yirga Cheffe, Papua New Guinea, Java Sunda, and Rwanda.
Keep at it. No one prefects it the first few times they roast, that's for sure.
Good Luck
B