1. I would spend a great deal of my time in this forum.
Meaning 1: past habit
In the past, I had a habit of spending a lot of time in this forum, but I don't do that anymore.
Meaning 2: conditional
I would spend a great deal of time in this forum, if ...
2a. I used to spend much
time of mine ...
2b. I used to spend much
of my time ...
______________ Correction
Yes!, not
Yes !
=> Do not put a space before the punctuation mark.