I started Tango and Ventura varieties from seeds for the first time this year. I also have overwintered plants of what turned out to be Chinese Celery that I bought starts for at the grower's co-op last year (I asked for celery and they found me the "last" 6-pack hiding among the parsley).
They took a little while to sprout -- about same wait as carrots I think. I started them early (10-12 wks before last frost was the instruction -- I'll look up exact dates in my notes if you want.... started on 2/16, ALL the Tango sprouted together on 2/24, Venture started sprouting on 2/23 and took about a week for them to all show up with a few no show.) and kept them on the bottom shelf -- cooler and less light than peppers or tomato seedlings. But I read that the main problem ith growing celery from seeds is that if the seedlings experience temps less than 55Â°F they have tendency to bolt the first year, so I kept them indoors with the peppers in the eary spring and put them outside on same temp conditions.
I started them in 3/4" micro soilblocks. They grew very well upblocked to 2" soil blocks. Others uppotted and growing in re-purposed K-cups (6 holes) did well also. I fed them diluted, aerated higher N organic fertilizer tea.
Peppers were hardened to direct sun, but I kept the celery seedlings in the noonday shade area, and planted them where they get a lot of moisture and shaded by the tomatoes.
Two of the Chinese Celery bolted last year and I let them go to seed and collected a bagful of celery seeds. This year, the bed is COVERED with volunteers and I'm hoeing them out like weeds.... The overwintered plants are bolting now, so I'll have plenty of volunteers next year too.
I'm going to try the Redventure variety with red stalks next year.
...so yeah. I'd say it was pretty easy. Only real problem I had was that my house gets invaded by ants at spring thaw -- fact of life -- and they pastured aphids on my celery seedlings every day -- one or two on each.
I was patiently picking aphids off with a bamboo skewer dipped in sudsy water and occasionally resorting to spraying with the soapy water, but mostly spraying down the marching ant trail.