Kenwag, sorry that the others made fun of you. Your question reveals that you are very new to the game, but you never denied that, so it is ok. We should avoid letting this forum deteriorate to another elitist bragger RTSanctuary.
Generally, you should never compare strat vs AI with strat vs humans. The AI cheats and generally plays very different from a human. Against a human, you need to play smart. Against the AI, you need to know and exploit its foolishness. This is a very different style of playing, and practising vs AI will actually cause you to mis-learn the game if you ever plan on playing vs human.
Your proposal already reflects this. You plan on winning with only 2/3 of your army against his full army because you construct some towers at your fb and expect him to attack you there. The AI probably will, but a human player will not attack you where you are strongest. He will circumvent your fb and hit you in the balls, i.e. your economy. He will raid your hunters and chubbies and destroy your rear TCs.
Towers at your fb are an expensive investition anyway. While there are situations in which they make sense, often enough they are money with which your opponent makes more troops or advances an age. Since your towers are useless everywhere but at the place where they are located, this can easily give him an edge over you.
Doing a rear attack (or raid) with a part of your army
(you said 1/3) is basically not a bad thing. In most cases you will want to attack his economy though, unless you are really sure your force is strong enough to take down his TC before defenders show up. You should definitely begin this rear raiding way before you can mount such a strong force. A combat group of 6 RC cannot defeat a TC, but is excellently-suited to attack his hunters and woodcutters and generally cause havoc in his economy.Quoted from kenwag:
My question is, I need advice on which units to pick to take out his TC. Which norse unit is the best to use against Town center fire etc?
Rams, especially Baldr rams, are best for this purpose for obvious reasons. If you want to attack him at an earlier time (which is strongly advisable especially for Loki), Einherjars and all sorts of giants are your friends. Mountain giants are especially effective against buildings, but other giants will do the job, too.
Darkness is a state of mind
Valor is the contempt of Death and Pain. (Tacitus)
Problems worthy of attack prove their worth by hitting back. (Piet Hein)