Im moving my business to a larger office space, and have seen…

I'm moving my business to a larger office space, and have seen something I like -- 750 sq ft just west of downtown Toronto (district C01 on the TREB map, FYI!). The real estate agent is preparing an offer to lease. I'm seeking professional advice to help me put in a good offer.

According to July real estate news, the downtown office vacancy rate is 5.9% and availability rate 8.4%. The vacancy rate has been falling; the papers are saying that the market is performing well. In June, the average cost psf for Toronto office space was $12.17. In July this had dropped to $10.81. I can't find a source providing detail by district; needless to say in a city this size you can find just about anything, so the average isn't specifically helpful.

The landlord is asking $21 psf. The agent is saying that he recently dropped the price from $23, and that this is the best price in the area... hard to confirm from listings because they don't all specify both size & asking price. However, from the research I've done this seems reasonable.

What I've discussed with the agent is the following:
- 5 yrs + a 5 yr option (I was in my last office for 15 yrs)
- first & last payable upon signing
- floors refinished
- build an interior wall with a window & a door
- repaint
- a couple of minor repairs
- 3 months' free rent
- drop the rate to $20.50

Do you have some familiarity with the Toronto market?

How can I find out what the "going rates" are for offers? I don't want to under- or over-ask.

How important is it for me to have the offer reviewed by a lawyer? Or perhaps another real estate agent?

Do you have any general advice for this sort of situation?

Thank you for your help!