Muggle // 0 (Can post an introduction, but cannot start posts in other forums)
Squib // 5
First Year // 20
Second Year // 100
Third Year // 200
(eligible for admission to Hogsmeade?)
Fourth Year // 400
Fifth Year // 700
I have no problem with the above. ...and maybe this isn't too bad??? 500 posts to get here: Househead 5th Year // 1200 then
400 posts to get here
ixth Year // 1800 then 
700 posts (What the?) :Househead 6th Year // 2500 then 
-------------------------------------------------------- But I don't like what comes next! 
1500 more posts Seventh Year // 4000 then
2000 ...more Prefect // 6000 then
2000 ...more Hogwarts Graduate // 8000 then
2000 ...more Ministry of Magic // 10,000
This seems like a massive time comittment before you graduate and a bit of a turn off ...if you like climbing a ladder ... albeit in this fantasy world.
If you only lower a few levels .... I'd ask you to change from 7th year upwards ...like...I don't know .... x3 posts a day x 365 days ...or something.