(1) 重くて赤いかばん / このかばんは重くて赤い
(2) 重く、赤いかばん / このかばんは重く、赤い。
Both expressions are valid, though (1) sounds more colloquial than (2).
For (2) You need to add 、 after the adjective except the last one.
(1) does not need 、 thanks to て which punctuate the two adjectives.
You can put more than two adjectives. (Of course it is OK to put 、if you want.)
e.g.
赤くて丸くておいしいくだものは?
I don't think it is grammatical to put two or more adjectives without conjugation. i.e. 重い赤いかばん.
すごい is adjective and to use it to modify not noun but adjective/verb, you have to change it to すごく.
However, すごい is used as adverb quite often, especially in conversation, even though it is ungrammatical.
"Wilder" version is すげえ, you'll find it often particularly in boy's speech.
I don't recommend to use it, but just for your reference.