I play Seaforge solely. I am not a super competitive person either so take what I say with a grain of salt.
You can not go wrong with Forge Guard. They are amazing! I have 1 full unit or 2 min units that I can make. I like to run min as they usually kill what ever I charge before the whole 10 man unit gets to attack.
Thor Steinhammer is a almost must in every list. He is so useful.
A couple of Grunback blasters are a good option as well. Having a spray template that you can boost all attack and damage rolls with is priceless. Thor works well with one of the marshaled as well.
Herne & Jonne are a great unit to get. Throwing out 3x3" templates a turn is great to help deal with weak infantry or infantry with stealth.
If you want another caster Ossrum is awesome. His Tier list is great and he is a great support caster. He helps Hammerfall with snipe also can help the Ogrun assault Coprs with snipe as well. Fire for effect is really nice if you add Herne & Jonne. His feat is great as well.
I personally like the Wroughthammer rockram jack. It weapons is really nice to boost and try to get the critical on. And with Ossrum you can snipe with it to give it a respectable 12" range. The hammer is pretty nice to with help from gorten and his
str boost.
Brun & Lug are a nice addition to seaforge as well. It helps with adding the fury into a warmachine game and Lug is pretty terrifying.
If you do get hammerfall be sure to get the
UA for them as well. They are a big help to that unit.
Ogrun Assault Corps are kind of fun as well.
I have yet to use the Tactical arcanists but they seem to be a nice addition to the seaforge.
Oh and our Colossal is mean, I have yet to buy one or use it as I am not a fan of the model. But stats and with what our casters can do. I really want to get one. I just need to figure out how to make it better looking.
I hope this has helped. I really like playing seaforge. They are a fun army to play, we could use another 2 point solo.