The TR Tourist visa gets you stamped into the Country for 60 days. You can apply in Country for a further 30 days extention of stay at a cost of 1900bt.
If the Embassy/Consulate dont want onward travel, Immigration may ask for it(it's an entry requirement but rarely asked for), the airline you're flying with will DEFINATELY want it.
You can apply for a tourist visa from any country. You just need to prove you entered and are residing legally in that country, ie upload a copy of your entry stamp/visa of the country you're applying from.
The Company/Organization you'll be working for should supply documents for your visa and work permit, ie a contract of employment. The cost for the Non Imm B visa is 2000bt, cost for 1 year extention of stay is 1900bt and I believe the cost of a work permit is 3800bt