Unless your compost gets so hot it kills all weed seeds I would not use as part of your seed compost as this needs to be sterile, otherwise you are going to have weeds coming up with your flower/veggie seedlings.

Absolutely MG. I personally use multi - purpose for all my seeds, and occasionally sieve it, saving the bigger lumps for potting on. I do add perlite to the seeding compost.

The best use for your garden compost (assuming its been produced by just putting stuff on it and letting it rot in its own time) is on the garden itself - I wouldn't even use it as ordinary potting compost, and its definitely not suitable for use as seed compost, as MG above says.

Agree with all above. I buy 'seed and potting compost' and use 2 parts of that to 1 part vermiculite, and it works :))